Esters of α-methyl-3,4-OR-phenylalanines

ABSTRACT

Derivatives of α-methyl-3,4-dihydroxyphenylalanine which are useful in compositions as anti-hypertensive agents.

This is a division of copending application Ser. No. 668,021, filed Mar.18, 1976, now U.S. Pat. No. 4,058,530 which in turn is a division ofapplication Ser. No. 482,102, filed June 25, 1974 now U.S. Pat. No.3,983,138, issued Sept. 28, 1976, which in turn is acontinuation-in-part of Ser. No. 400,609, filed Sept. 25, 1973, nowabandoned.

The present invention relates to a novel and useful class of compoundsand the use of a compounds in the treatment of hypertension. Moreparticularly, it relates to derivatives ofα-methyl-3,4-dihydroxyphenylalanine.

It has been suggested in the art that various alanine compounds may beuseful in the treatment of hypertension (see U.S. Pat. No. 2,868,818).It is further known in the art that hypertension is preferably treatedwith L-α-methyl-3,4-dihydroxyphenylalanine since the D-form of thecompound is therapeutically inert and only the L-form is therapeuticllyactive. The removal of the D-form thereby lessens toxicity and increaseseffectiveness (see U.S. Pat. No. 3,344,023 and British Patent No.936,074). The L-isomer of α-methyl-3,4-dihydroxyphenylalanine iscommonly referred to as L-α-methyldopa or methyldopa. It is stillfurther known in the art that the alkyl esters of L- orDL-α-methyl-3,4-dihydroxyphenylalanine are useful in the emergencytreatment of hypertension by parental administration (see U.S. Pat. No.3,230,143). It has now been found that other esters and derivatives ofDL- or L-α-methyl-3,4-dihydroxyphenylalanine having specific structuresare also active in the treatment of hypertension therely givingalternative compounds for such treatment. It has also been found thatsome of the new compounds have a much higher activity and thus require alower dosage than the known compounds.

Accordingly, it is an object of the present invention to provide a noveland useful class of compounds which are active in treating hypertension.A further object is to provide a more active group of compounds for thetreatment of hypertension. A still further object is to provide a methodof producing such compounds. Another object is to provide a method oftreatment for hypertension by the use of the new compounds. Anotherobject is to provide a novel and useful composition for the treatment ofhypertension. Other objects will become apparent as the description ofthe invention proceeds.

These objects are accomplished by the present invention which provides acompound of the formula ##STR1## wherein N IS 0, 1, 2 OR 3;

M is 0, 1, 2 or 3;

A₁ and A₂ are individually H or a lower all anoyl group;

R₁ and R₂ are individually H or alkyl of 1 to 3 carbon atoms and;

R₃ is selected from the group consisting of

(A) a monocyclic or bicyclic heterocyclic radical containing from 3 to12 nuclear carbon atoms and 1 or 2 nuclear hetero atoms selected from Nand S with at least one being N, and with each ring in the saidheterocyclic radical containing 5 to 6 members and

(B) the radical X--R₄

wherein X is --O--, --S-- --NH-- and

R₄ contains up to 21 carbon atoms and is (1) a hydrocarbon radical or(2) an acyl radical of an organic acylic or monocyclic carboxylic acidcontaining not more than 1 hetero atom in the ring

or a pharmaceutically acceptable acid addition salt thereof.

In a preferred embodiment of the present invention, n and m are 0 or 1,A₁ and A₂ are H, R₁ and R₂ are hydrogen or methyl and R₃ is theheterocyclic ring ##STR2## which may be substituted by lower alkylgroups of 1 to 3 carbon atoms, or R₃ is --X--R₄ wherein X is --O-- or--NH-- and R₄ is an acyl radical from an alkanoic acid containing 2 to 5carbon atoms.

The present invention further provides an ester of the L isomer of anamino acid, substantially free of the D isomer, having the formula##STR3## or a pharmaceutically acceptable acid addition salt thereofwherein n, m, R₁, R₂ and R₃ are as defined above. With regard to the Lisomer, it should be noted that the asymmetric carbon atom is the onecontaining the amino and methyl group in the acid portion of themolecule. It is this portion of the molecule that is referred to asbeing in the L configuration. Note that the L configuration refers tothe stereo configuration and not to the optical rotation although inthis case the L stereo configuration is the 1 or levo form of theoptical isomer. However, it should also be noted that in some instanceswhen R₁ and R₂ are different groups the carbon atom to which they areattached is also an asymmetric carbon atom and can thus exist in eitherthe L or D configuration. As is hereinafter pointed out, both of theisomers of this portion of the compound are active. As is furtherpointed out, these stereo isomers have been separated but their stereoconfiguration has not been determined so they are merely designated asthe α and β isomer. In any event, both the α and β isomers are activeregardless of their stereo configuration.

The present invention still further provides a method of treatinghypertension in a hypertensive animal which comprises administering tothe animal a therapeutically effective amount of a compound of theformula ##STR4## or a pharmaceutically acceptable acid addition saltthereof wherein n, m, A₁, A₂, R₁, R₂ and R₃ are as defined above.

In the treatment of hypertension, the compounds of the present inventionare generally administered in amounts of from about 0.005 to about 300mg./kg. of body weight of the animal and preferably from about 0.05 toabout 100 mg./kg. In a still more preferred embodiment, the compoundsare administered in amounts of from about 0.1 to about 25 mg./kg. ofbody weight of the animal. In this regard, it should be noted that thedosage must be adjusted depending upon the activity of the compound, theresponse desired in the reduction of blood pressure and also the weightof the animal. In the ranges given above, the more active compoundswould tend to be given at the lower dosages and the less activecompounds at the higher dosages.

The present invention also provides a method of treating hypertension ina hypertensive animal which comprises administering to the animal atherapeutically effective amount of an ester of the L isomer of an aminoacid, substantially free of the D isomer, having the formula ##STR5## ora pharmaceutically acceptable acid addition salt thereof wherein n, m,R₁, R₂ and R₃ are as defined above.

When the L isomer of a compound of the present invention is given in thesubstantial absence of the D isomer, the required dosage of the L isomeris approximately one-half of that of the racemate since the D isomer istherapeutically inactive. However, the compounds of the presentinvention vary in activity to some degree and thus the racemate of oneof the less active compounds of the present invention may requireseveral times the dosage of a more active compound. In general, thecompounds will be administered within the above dosages.

The present invention also provides a pharmaceutical compositioncomprising an inert pharmaceutically acceptable diluent and a compoundof the formula ##STR6## or a pharmaceutically acceptable acid additionsalt thereof wherein n, m, A₁, A₂, R₁, R₂ and R₃ are as defined above.

In a single dosage form of the composition of the present invention, theactive compound is generally present in the composition in amounts offrom about 1 mg. to about 2,000 mgs., more preferably about 5 mgs. toabout 1,000 mgs. In a still more preferred embodiment, the activecompound is present in amounts of from about 10 mgs. to about 500 mgs.The single dosage form of the compound may be administered in a singleslow acting dose or it may be administered in several small dosesthroughout the day, generally 2 to 8 individual dosages.

The present invention also provides a pharmaceutical compositioncomprising an inert pharmaceutically acceptable diluent and an ester ofthe L isomer of an amino acid, substantially free of the D isomer,having the formula ##STR7## or a pharmaceutically acceptable acidaddition salt thereof wherein n, m, R₁, R₂ and R₃ are as defined above.

As in the method of treatment, reduced dosages of the L isomersubstantially free of the D isomer are required as compared to theracemate. However, the difference in activity of various compoundsrequires the use of different dosages. In some instances, the compoundsare many times more active than others and thus the racemate of one mayrequire even less of a dosage than the L isomer of a second. In general,however, the dosages will be within the above ranges.

The present invention further provides a process for preparing acompound of the formula ##STR8## wherein n is 0, 1, 2 or 3;

m is 0, 1, 2 or 3;

A₁ and A₂ are individually H or a lower alkanoyl group;

R₁ and R₂ are individually H or alkyl of 1 to 3 carbon atoms and;

R₃ is selected from the group consisting of

(A) a monocyclic or bicyclic heterocyclic radical containing from 3 to12 nuclear carbon atoms and 1 or 2 nuclear hetero atoms selected from Nand S with at least one being N, and with each ring in the saidheterocyclic radical containing 5 to 6 members and

(B) the radical X--R₄

wherein X is --0--, --S-- or --NH-- and

R₄ contains up to 21 carbon atoms and is (1) a hydrocarbon radical or(2) an acyl radical of an organic acyclic or monocyclic carboxylic acidcontaining not more than 1 hetero atom in the ring

or an acid addition salt thereof which comprises

(a) the hydrolysis or reduction of an acid derivative of the formula##STR9## or an acid addition salt thereof wherein n, m, R₁, R₂ and R₃are as defined above and R₅, R₆ and R₇ are hydrogen or a blocking groupwith at least one being a blocking group; or

(b) the esterification of an acid derivative of the formula ##STR10## oran acid addition salt thereof with a compound of the formula ##STR11##wherein Y is --COOH, --COhalogen or -carboxylic acid salt and n, m, A₁,A₂, R₁, R₂ and R₃ are as defined above and X₁ is hydroxyl, alkali metal--O--, halogen or a substituted --SO₃ -- group; or

(c) the reduction of a compound of Formula I wherein R₃ contains one ormore reducible groups; or

(d) the reaction of a compound of the formula ##STR12## wherein n, m,A₁, A₂, R₁ and R₂ are as given above and Z is --OH, --SH, halogen,substituted --SO₃ -- group or --NH₂ with an acylating agent; R₃ --H orR₃ --alkali metal wherein R₃ is as defined above; or

(e) the cyclization of a compound of the formula ##STR13## wherein n₁ is1, 2 or 3; A₁, A₂, R₁, R₂, n and m are as defined above

with an acylating agent

and, if desired, separating the stereoisomers by (1) fractionalcrystallization of one stereoisomer from solution or (2) formingdiastereomers with an optically active acid and crystallizing one of thediastereomers from the solution.

The present invention further provides a process for preparing acompound of the formula ##STR14## or an acid addition salt thereofwherein n, m, R₁, R₂ and R₃ are as defined above which comprises thehydrolysis or reduction of an acid derivative of the formula ##STR15##or an acid addition salt thereof wherein R₅, R₆ and R₇ are individuallyhydrogen or a blocking group with at least one being a blocking group.The hydrolysis or reduction is carried out under conventionalconditions.

The present invention further provides a process for preparing acompound of the formula ##STR16## or an acid addition salt thereofwherein n, m, R₁, R₂ and R₃ are as defined above which comprises theesterification of an acid derivative of the formula ##STR17## or an acidaddition salt thereof with a compound of the formula ##STR18## wherein Yis --COOH, --COhalogen or -carboxylic acid salt and n, m, R₁, R₂ and R₃are as defined above and X is hydroxyl, alkali metal --O--, halogen or asubstituted --SO₃ -- group. The esterification is carried out underconventional reaction conditions.

In a preferred embodiment of the present invention, the process iscarried out with the amino acid portion of the molecule being in the Lstereo configuration.

The expressions "(--CH₂)_(n) " and "(--CH₂)_(m) " also include thebranched chain alkylene radicals such as ##STR19## Preferably n and mare 0 or 1.

The terminology "a monocyclic or bicyclic . . . 5 to 6 members" meansthat the compounds contain one or two ring nitrogen atoms with anoptional ring sulfur atom and from 3 to 12 ring carbon atoms. Thecompounds further contain one or two rings with 5 or 6 members in eachring and the rings may be substituted by such groups as halogen,hydroxyl, amino or other such groups.

The terminology "R₄ contains up to 21 carbon atoms . . . 1 hetero atom"signifies that R₄ contains a total of from 1 to 21 carbon atoms and iseither a hydrocarbon radical or an acyl radical of the formula ##STR20##wherein R is an acyclic or a monocyclic radical with not more than 1hetero atom. As is hereinafter pointed out in the examples, the R groupmay be an alkyl group, a heterocyclic radical or any other such radical.The nature of this R group does not appear to be critical and it may bewidely varied.

The expression "pharmaceutically acceptable acid addition salt" is anexpression well known in the art and includes those compounds which aremade by the reaction of the free base with an inorganic or organic acid.It includes the hydrochloride, the hydrobromide, salts with sulfuricacid and the like.

The phrase "the L isomer of an amino acid, substantially free of the Disomer" means that the D isomer is present in amounts not exceedingabout 10%. However, it is desirable that the D isomer be substantiallyabsent from the composition. In the examples which follow, when the Lisomer is designated, the compound is substantially 100% (i.e. well over99%) in the L configuration.

The terminology "blocking group" signifies any group which will protectthe amino or hydroxyl groups during the reaction. Among the suitableblocking groups for the nitrogen atom are carbobenzyloxy,para-methoxycarbobenzyloxy, trifluoroacetyl, HCl and the like. Suitableblocking groups for the hydroxyl group are diphenyl ketal for bothhydroxyl groups and the acetyl and carbobenzyloxy for the individualhydroxyl groups as well as other such radicals. The substitutent in the"substituted --SO₃ -- group" can be substantially any radical sincethese groups are readily cleaved during the esterification reaction andthe nature of the group is not at all critical.

The term "reducible groups" signifies any group which can be replaced bythe hydrogen atom or can be partially or completely saturated byhydrogen. Such groups include --CH═CH--, --C.tbd.C--, -halogen, --NO₂,--CN and the like.

The expression "acylating agent" designates an activated carboxylic acidderivative such as a carboxylic acid anhydride (including mixedanhydrides) or a compound of the formula ##STR21## wherein R₈ is anorganic radical and X₂ is an easily removable group such as halogen,p-nitrophenoxy, phenoxy or the like.

When racemic mixtures are formed in accordance with the synthesis of thepresent invention, it is sometimes desirable to separate the mixturesinto their L and D isomers. The isomers can be separated at any point inthe synthesis and in most instances it is desired to separate them priorto forming the final product. In other instances (as when R₁ and R₂ aredifferent groups and the acid portion is in the L configuration), amixture of diastereomers is formed as the final product and these may bedirectly separated by crystallization or the formation of simplederivatives with crystallization. It is by far preferable, however, tostart with the desired isomer (i.e. the L isomer) when the single isomeris desired. It is also possible to form a diastereomer of the racemicmixtures formed in accordance with the present invention to effectseparation. In such instances, an optically active acid such as tartaricacid, 10-camphor sulfonic acid, malic acid, pyroglutamic acid, menthoxyacetic acid and the like may be used. The selection of the particularacid may be made as desired and would be obvious to one skilled in theart.

The compounds of the present invention can be used in the form ofcompositions preferably administered in unit dosage form such astablets, pills, capsules, powders, granules, sterile parenteralsolutions or suspensions, oral solutions or suspensions and the like.For preparing solid compositions such as tablets, the principal activeingredient is mixed with conventional tableting ingredients such as cornstarch, lactose, sucrose, sorbitol, talc, stearic acid, magnesiumstearate, dicalcium phosphate, gums and fractionally similar materialsas pharmaceutical diluents or carriers. The tablets or pills of thenovel compositions can be laminated or otherwise compounded to provide adosage from affording the advantage of prolonged or delayed action orpredetermined successive action of the enclosed medication. For example,the tablet or pill can comprise an inner dosage and an outer dosagecomponent, the latter being in the form of an envelope over the former.The two components can be separated by an enteric layer which serves toresist disintegration in the stomach and permits the inner component topass intact into the duodenum or to be delayed in release. A variety ofmaterials can be used for such enteric layers or coatings, suchmaterials including a number of polymeric acids or mixtures of polymericacids with such materials as shellac, shellac and cetyl alcohol,cellulose acetate and the like. A particularly advantageous entericcoating comprises a styrene maleic acid copolymer together with knownmaterials contributing to the enteric properties of the coating. Thecompounds are also useful when administered in the form of suppositoriesor with a penetrant such as dimethyl sulfoxide.

The liquid forms in which the novel composition of the present inventionmay be incorporated for administration include suitably flavoredemulsions with edible oils, such as, cottonseed oil, sesame oil, coconutoil, peanut and the like, as well as elixirs and similar pharmaceuticalvehicles. Suitable dispersing or suspending agents for aqueoussuspensions include synthetic and natural gums, such as, tragacanth,acacia, alginate, dextran, sodium carboxymethylcellulose,methylcellulose, polyvinylpyrrolidone, gelatin and the like. Sterilesuspensions or solutions are required for parenteral use. Isotonicpreparations containing suitable preservatives are also highly desirablefor injection use.

The term single dosage form as used in the specification referes tophysically discrete units suitable as unitary dosage for warm-bloodedanimal subjects, each unit containing a predetermined quantity of activematerial calculated to produce the desired therapeutic effect inassociation with the required pharmaceutical diluent, carrier orvehicle. The specifications for the novel single dosage forms of thisinvention are dictated by and are directly dependent on (a) the uniquecharacteristics of the active material and the particular therapeuticeffect to be achieved, and (b) the limitations inherent in the art ofcompounding such an active material for therapeutic use in warm-bloodedanimals as disclosed in detail in this specification. Examples ofsuitable oral single dosage forms in accord with this invention aretablets, capsules, pills, powder packets, granules, wafers, cachets,teaspoonfuls, dropperfuls, ampules, vials, segregated multiples of anyof the foregoing, and other forms as herein described.

The following examples are given to illustrate the invention and are notintended to limit it in any manner. All parts are given in parts byweight unless otherwise expressed. The "reduced pressure" employed inthe following examples is 15 to 25 mm. Hg at 25° to 35° C. (unlessotherwise indicated). When reduced pressure is employed to remove asolvent, the resultant product is oftentimes a solvate and thus theexample refers to the formation of a "concentrated" product although allof the solvent has been removed with the exception of that bound in theproduct.

EXAMPLE 1 A. Preparation ofL-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine hydrochloride

A mixture of 19.3 g. (0.0777 mole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine hydrochloride [L-α-methyldopahydrochloride] and 37 g. (0.156 mole) of dichlorodiphenylmethane isimmersed with slow stirring in a preheated oil bath at 190° C. Afterreaction has started, as evidenced by vigorous gas evolution, thereaction mixture is stirred rapidly for six minutes at 190° C. removedfrom the hot oil bath and allowed to cool to 25°-30° C. The crudeproduct from 12 runs is combined, slurried with 3 l. of diethyl etherfiltered, washed with an additional 2 l. of diethyl ether and dried at30° C. under 50 mm. pressure. Recrystallization is accomplished bydissolving the product in ethanol and adding ethyl acetate toprecipitate the product. The procedure gives 255 g. (66.4%) ofL-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine hydrochloride,m.p. 267°-268° C. dec.

Anal. calcd. for C₂₃ H₂₁ NO₄ HCl: C, 67.07; H, 5.39; N, 3.40. Found: C,66.91; H, 5.29; N, 3.34.

B. Preparation ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine

A mixture of 175 g. (0.425 mole) ofL-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine hydrochloride,1750 ml. of acetone and 1750 ml. of water is stirred under nitrogen at atemperature below 10° C. while the pH is adjusted to 12.0 by the slowaddition of a 10% sodium hydroxide solution. Carbobenzyloxy chloride, 93g. (0.545 mole) is added dropwise over 5-7 minutes to the reactionmixture at 20°-30° C. accompanied by the simultaneous addition of a 10%sodium hydroxide solution to maintain a pH of 12.0-12.2. After additionof the carbobenzyloxy chloride is complete, the reaction mixture isstirred at 25°-30° C. for three hours. Most of the acetone is thenremoved under reduced pressure at 25° to 35° C. to precipitate thesodium salt of the desired N-carbobenzyloxy derivative. The sodium saltis extracted into 1.5 l. of ethyl acetate, washed with 200 ml. of 5%sodium hydroxide solution and 200 ml. of a saturated sodium chloridesolution and then dried over magnesium sulfate. After adding 17.5 g. ofdecolorizing carbon and filtering through a magnesium sulfate pad,solvents are removed under reduced pressure at 25° to 35° C. The residueis slurried two times with 1 l. of a 20% ethyl ether-80% hexane (byvolume) solution and filtered to give the sodium salt of the desiredN-carbobenzyloxy derivative. This sodium salt is dissolved in 1.5 l. ofethyl acetate, cooled to 10° C. and acidified to pH 2 with 6 Nhydrochloric acid. The ethyl acetate extract is washed with 200 ml. of asaturated sodium chloride solution, dried over magnesium sulfate,filtered and concentrated under reduced pressure at 25° to 35° C. TheN-carbobenzyloxy derivative is dried further at 25°-30° C. and 0.2-0.3mm. Hg to give 169 g. (78.0%) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine.

C. Preparation of succinimidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 13.5 g. (0.0265 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,2.7 g. (0.027 mole) of triethylamine and 5.19 g. (0.029 mole) ofN-bromomethylsuccinimide in 35 ml. of dry dimethylformamide is stirredat 25°-30° C. for 16 hours. The reaction mixture is poured into 400 ml.of ice water and the product extracted into 200 ml. of a 50%chloroform-50% diethyl ether (by volume) mixture. The organic extract iswashed with 50 ml. of a dilute (5%) sodium carbonate solution and 50 ml.of a saturated sodium chloride solution and then dried over anhydrousmagnesium sulfate to remove water. After filtering and concentratingunder reduced pressure, the residue is recrystallized. Recrystallizationis accomplished by dissolving the product in ethanol and adding hexaneto precipitate the product. The process gives 12.1 g. (73.6%) ofsuccinimidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxy)phenyl)-2-methylalaninate,m.p. 143.0°-145.0° C.

Anal. calcd. for C₃₆ H₃₂ N₂ O₈ : C, 69.66; H, 5.20; N, 4.51. Found: C,69.83; H, 5.14; N, 4.52.

D. Preparation of succinimidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate

A suspension of 6.6 g. (0.0106 mole) of succinimidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 180 ml. of absolute ethanol and 9 ml. of a 9.6 N ethanolic-anhydroushydrogen chloride solution is hydrogenated with 3.3 g. of a 10%palladium-on-carbon catalyst at an initial pressure of 30 p.s.i. untilhydrogen uptake is complete. After removal of catalyst by filtration,the filtrate is concentrated under reduced pressure. The residue isextracted with 50 ml. of benzene and then 50 ml. of ethyl acetate. Theinsoluble solid is then shaken with 50 ml. of a 10% ethanol-90% ethylacetate (by volume) mixture and 10 ml. of a saturated sodium carbonatesolution. After filtration, the filtrate is dried over anhydrousmagnesium sulfate, filtered and concentrated under reduced pressure. Theresidue is redissolved in 25 ml. of absolute ethanol, treated with 5 ml.of a 9.6 N ethanolic-anhydrous hydrogen chloride solution andconcentrated under reduced pressure to give 2.5 g. (62.7%) ofsuccinimidomethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride hydrate, homogeneous upon thin layer chromatography[fluorescent silica gel plate, 30% methanol-70% benzene (by volume)solvent] with an observed Rf = 0.5.

Anal. calcd. for C₁₅ H₁₈ N₂ O₆.HCl.H₂ O: C, 47.81; H, 5.62; N, 7.44.Found: C, 48.09; H, 5.74; N, 7.42.

EXAMPLE 2 A. Preparation of N-(1-chloroethyl)-succinimide

N-vinylsuccinimide, 50.0 g. (0.40 mole) is dissolved in 1000 ml. carbontetrachloride, 5.20 g. (0.020 mole) of stannic chloride is added and themixture is stirred while saturating with hydrogen chloride for 6 hoursat 20°-30° C. After 24 hours, the mixture is resaturated with hydrogenchloride for 1.5 hours. At the end of 48 hours, the solution is decantedand the gummy residue is washed with ten 100 ml. portions of carbontetrachloride. The combined extracts are slurried with 10 g. ofdiatomaceous earth, filtered and the filtrate concentrated under reducedpressure to approximately 400 ml. The N-(1-chloroethyl)-succinimide isfiltered and dried at 20°-30° C. under reduced pressure to yield 38.4 g.(59%) of white solid melting at 83.5°-84.5° C.

B. Preparation of α-succinimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A mixture of 30.66 g. (0.060 mole)L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,9.70 g. (0.060 mole) of N-(1-chloroethyl)succinimide, 6.07 g. (0.060mole) of triethylamine and 75 ml. of dry dimethylformamide is stirred at95° for 19 hours. The reaction mixture is poured into 750 ml. of waterand the product extracted into three 500 ml. portions of ethyl acetate.The combined organic extracts are washed with three 300 ml. portions of5% sodium hydroxide solution. Then three times with 300 ml. of asaturated sodium chloride solution and dried over anhydrous magnesiumsulfate. After filtering, the solution is treated with 5 g. of charcoal,filtered and the solvent is evaporated under reduced pressure to give37.90 g. (99%) of α-succinimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninateas a mixture of diastereomeric isomers (α and β).

C. Preparation of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A suspension of 20.18 g. (0.032 mole) of α-succinimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 275 ml. of 25% absolute ethanol-75% ethyl acetate (by volume)solution is hydrogenated with 8.5 g. of 10% palladium-on-carbon catalystat an initial pressure of 40 p.s.i. and room temperature for 23 hours.The catalyst is filtered and the filtrate evaporated under reducedpressure at 30° to 40° C. The residue is dissolved in 250 ml. of 10%ethanol-90% ethyl acetate (by volume) solution and stirred with 20 ml.of saturated sodium carbonate solution and approximately 30 g. ofanhydrous sodium carbonate for 10 minutes. After filtration, thefiltrate is dried over anhydrous magnesium sulfate, filtered andevaporated to dryness under reduced pressure. The residue is dissolvedin 130 ml. of dry chloroform, the solution is cooled in an ice bath andsaturated with hydrogen chloride for 15 minutes. The solid is collected,washed by suspension in 100 ml. of anhydrous ether three times and thenslurried in 300 ml. of ethyl acetate under N₂ in a stoppered flask atroom temperature overnight. The α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride is collected,stirred in 300 ml. of hexane for 2 hours and dried in a vacuumdesiccator over CaCl₂ to give 8.32 g. (62%) of hydrochloride as amixture of α and β isomers, observed Rf = 0.7 upon thin layerchromatography [fluorescent silica gel plate, 50% methanol-50% benzene(by volume) solvent].

Anal. calcd. for C₁₆ H₂₀ N₂ O₆.HCl.1/2 CH₃ CO₂ C₂ H₅ : C, 51.86; H,6.05; N, 6.7. Found: C, 51.98; H, 5.87; N, 6.65.

EXAMPLE 3 A. Separation of α-succinimidoethylL-N-carbobenzyloxy-3-(3,4-dihydroxyphenylmethylenedioxyphenyl)-2-methylalaninateisomers

The mixture of diasteromeric isomers of Example 2, 150.5 g., isdissolved in a boiling mixture of 1200 ml. of benzene and 100 ml. ofabsolute methanol, filtered and the filtrate is concentrated to a volumeof approximately 700 ml.. Absolute methanol, 100 ml., is added to thesolution, which then is diluted to cloudiness with 1000 ml. of hexane,seeded and scratched to induce crystallization. The mixture is cooled at5° C. for about 16 hours and the crude crystalline α-isomer is thencollected, washed by suspension in 200 ml. of a 50:50 mixture (byvolume) of benzene and hexane and dried at 70° C. The product weighs68.1 g. and melts at 185.5°-191° C. An analytical sample melts at199.5°-201.5° C. after two additional recrystallizations.

Anal. calcd. for C₃₇ H₃₄ N₂ O₈ : C, 70.02; H, 5.40; N, 4.41. Found: C,70.22; H, 5.52; N, 4.29.

The combined mother liquors and washings from the α-isomer areevaporated to dryness under reduced pressure at 60° C. to give 79.3 g.of the β-isomer as a very viscous oil.

B. Preparation of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride dihydrate(β-isomer)

A solution of 10.0 g. (0.016 mole) of α-succinimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate(β-isomer) in 140 ml. of 25% absolute ethanol-75% ethyl acetate (byvolume) solution is hydrogenated with 4.2 g. of 10% palladium-on-carboncatalyst at an initial pressure of 40 p.s.i. and room temperature for 20hours until hydrogen uptake is complete. The catalyst is filtered undernitrogen, the filtrate is acidified with 2.0 ml. of 9.4 N ethanolichydrogen chloride and evaporated to dryness under reduced pressure at30° to 40° C. The amorphous solid residue is dissolved in 50 ml. warm95% ethanol (5% water), filtered and the filtrate is diluted toincipient cloudiness with anhydrous ether (68 ml.), seeded and scratchedto induce crystallization. The product is collected and stirred in 300ml. of anhydrous ether to remove any diphenylmethane. After one hour,the solid is collected and dried at 70° C. overnight to give 3.7 g. ofmaterial melting at 123°-126° C. (dec.). Recrystallization from 20 ml.of 95% ethanol affords 3.36 g. (51%) of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride dihydrate(β-isomer) as the dihydrate melting at 129°-131° C. (dec.) (dried at 70°C. overnight), homogeneous upon thin layer chromatography [fluorescentsilica gel plate, 50% methanol-50% benzene (by volume) solvent], Rf =0.7.

Anal. calcd. for C₁₆ H₂₀ N₂ O₆.HCl.2H₂ O: C, 47.00; H, 6.16; N, 6.85.Found: C, 46.85, 47.09; H, 6.12, 6.16; N, 6.76, 6.61.

[α]_(D) ²⁴⁰ = + 33.46° (C = 1.5 CH₃ OH)

EXAMPLE 4 A. Preparation of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride (α-isomer)

A solution of 10.0 g. (0.016 mole) of α-succinimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate(α-isomer) in 140 ml. of 25% absolute ethanol-75% ethyl acetate (byvolume) solution is hydrogenated with 4.2 g. of a 10%palladium-on-carbon catalyst at an initial pressure of 40 p.s.i. androom temperature for 27-1/2 hours until hydrogen uptake is complete. Twoml. of a 9.4 N ethanolic solution of anhydrous hydrogen chloride isadded and the catalyst removed by filtration through a pad ofdiatomaceous earth. After concentrating under reduced pressure, theresidue is extracted by shaking with 200 ml. diethyl ether, twice with200 ml. benzene and finally twice with 200 ml. of diethyl ether. Thematerial remaining after these extractions is the desiredα-succinimidoethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride (α-isomer) diethyl ether solvate, Rf = 0.7 [thin layerchromatography fluorescent silica gel plate, 50% methanol-50% benzene(by volume) solvent] contaminated with 12% diphenylmethane.

[α]_(D) ²⁴ = -18.75 (C, 1.68, CH₃ OH).

EXAMPLE 5 A. Preparation of 2-trifluoroacetamidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 5.09 g. (0.010 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,1.01 g. (0.010 mole) of triethylamine and 1.76 g. (0.010 mole) ofN-(2-chloroethyl)-2,2,2-trifluoroacetamide in 20 ml. drydimethylformamide is stirred at 110° C. for 20 hours under nitrogen. Thecooled reaction mixture is poured into 500 ml. of ice water and theproduct extracted into three 500 ml. portions of ethyl acetate. Thecombined extracts are washed with 200 ml. of water, dried (MgSO₄),filtered and concentrated to an oil under reduced pressure. The residualoil is redissolved in 100 ml. ethyl acetate, extracted with two 50 ml.portions of a 5% sodium hydroxide solution, washed with 50 ml. of waterand dried over magnesium sulfate. Filtering and concentrating underreduced pressure gives 4.92 g. of an oil. Chromatography of this oil on200 g. of silica gel and elution with a 5% solution of methanol inchloroform affords 4.11 g. (63.4%) of the 2-trifluoroacetamidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninateas an oil, homogeneous upon thin layer chromatography [fluorescentsilica gel plate developed with 5% methanol-95% chloroform (by volume)]Rf = 0.8.

B. Preparation of 2-trifluoroacetamidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 2.0 g. (0.0031 mole) of 2-trifluoroacetamidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 125 ml. absolute ethanol and 1.0 g. of a 10% palladium-on-carboncatalyst is hydrogenated at room temperature and an initial pressure of36 p.s.i. for 5-2/3 hours until hydrogen uptake is complete. Catalyst isremoved by filtration under nitrogen through a diatomaceous earth filterpad and the filtrate is concentrated under reduced pressure at atemperature of 20° to 30° C. The residue is redissolved in 25 ml.absolute ethanol, converted to the hydrochloride by addition of 2 ml. of7.6 N ethanolic-anhydrous hydrogen chloride solution and thenconcentrated under reduced pressure. The residue is precipitated twiceby dissolving in ethanol and adding sufficient ethyl ether toprecipitate the product to give 800 mg. (66.6%) of2-trifluoroacetamidoethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride as the ethanol solvate, homogeneous upon thin layerchromatography [fluorescent silica gel plate developed with 50%methanol-50% chloroform (by volume)] RF = 0.8.

Anal. calcd. for C₁₄ H₁₇ F₃ N₂ O₅.HCl.C₂ H₅ OH: C, 44.40; H, 5.59; N,6.47. Found: C, 44.55; H, 5.29; N, 6.72.

EXAMPLE 6 A. Preparation of 2-nicotinamidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 5.84 g. (0.015 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,1.52 g. (0.015 mole) of triethylamine and 2.77 g. (0.015 mole) ofN-(2-chloroethyl)-nicotinamide in 20 ml. dry dimethylformamide isstirred under nitrogen at 95° C. for 20 hours. The cooled reactionmixture is poured into 200 ml. of ice water and the product extractedinto three 175 ml. portions of ethyl acetate. The combined extracts arewashed with 100 ml. of saturated sodium bicarbonate solution, 100 ml. ofwater and dried (MgSO₄). After filtering, solvents are removed underreduced pressure to give 6.28 g. (85%) of 2-nicotinamidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate,homogeneous upon thin layer chromatography [fluorescent silica gel platedeveloped with a 20% methanol-80% benzene (by volume) solution] observedRf = 0.45.

B. Preparation of 2-nicotinamidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate dihydrobromide

A mixture of 1.0 g. (2.0 mmole) of 2-nicotinamidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninateand 10 ml. of a 30-32% solution of anhydrous hydrogen bromide in aceticacid is allowed to stand at 20°-25° C. for 30 minutes until gasevolution is complete. The homogeneous solution is concentrated underreduced pressure at 20°-25° C. and the residue is stirred with 50 ml.diethyl ether for 3 days. The nearly white solid is collected, washedwith 50 ml. of anhydrous ethyl ether and dried under high vacuum (0.1 to0.3 mm. Hg.) at 20°-25° C. to give 600 mg. (77%) of the2-nicotinamidoethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatedihydrobromide, observed Rf = 0.5 upon thin layer chromatography[fluorescent silica gel plate developed with a solution consisting ofequal parts (by volume) of n-butanol, acetic acid, 1% aqueous sodiumbisulfite, benzene and acetone].

Anal. calcd. for C₁₈ H₂₁ N₃ O₅ :2HBr.2H₂ O: C, 38.79; H, 4.88; N, 7.54.Found: C, 38.79; H, 4.56; N, 7.37.

EXAMPLE 7 A. Preparation of α-chloroethylpivalate

Zinc chloride, 400 mg., is fused at 0.2-0.5 mm pressure and cooled to25°-30° C. under nitrogen. Pivaloyl chloride, 48 g. (0.40 mole) is addedto the fused zinc chloride followed by acetaldehyde, 19.2 g. (0.44mole). During addition of the acetaldehyde, which is done as rapidly aspossible, the reaction mixture is stirred and cooled to prevent loss ofacetaldehyde due to the exothermic nature of the reaction. After heatingat reflux for 1 hour, distillation gives 36 g. (55%) ofα-chloroethylpivalate, b.p. 32°-4° C. at 4 mm.

B. Preparation of α-pivaloyloxyethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

To a stirred solution of 9.0 g. (0.018 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninein 25 ml. dry dimethylformamide is added 1.80 g. (0.018 mole) oftriethylamine followed by 2.96 g. (0.018 mole) of α-chloroethylpivalate.After stirring at 90°-95° C. for 20 hours, the reaction mixture ispoured into 350 ml. water and the product extracted three times with 100ml. of ethyl ether. The ether extracts are combined, washed with 50 ml.of a 5% sodium hydroxide solution, 50 ml. of water and dried overanhydrous magnesium sulfate. After filtering, solvents are removed underreduced pressure to give 7.9 g. (68.9%) of crude α-pivaloyloxyethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate.

C. Preparation of α-pivaloyloxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 7.8 g. of α-pivaloyloxyethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 140 ml. absolute ethanol and 11 ml. of an 8 N ethanolic-anhydroushydrogen chloride solution is hydrogenated with 3.7 g. of a 10%palladium-on-carbon catalyst at 20°-25° C. and an initial pressure of 35p.s.i. for 19 hours until hydrogen uptake ceases. After removingcatalyst by filtration, ethanol is removed under reduced pressure. Theresidue is stirred overnight with 80 ml. benzene. The benzene is removedby decantation, replaced with 80 ml. of hexane stirred and the hexanedecanted off. The residue is dissolved in 300 ml. ethyl acetate, stirredbriefly with a mixture of 5 g. of solid sodium carbonate and 5 ml.saturated sodium carbonate solution and dried over anhydrous magnesiumsulfate. After filtering, 3 ml. of 9.6 N ethanolic-anhydrous hydrogenchloride is added and the solution concentrated under reduced pressureto dryness. Further drying at 65° C. and 0.2 mm. pressure gives 2.16 g.(47.2%) of the α-pivaloyloxyethyl ester hydrochloride.

Anal. calcd. for C₁₇ H₂₅ NO₆.HCl: C, 54.32; H, 6.97; N, 3.73. Found: C,54.47; H, 7.36; N, 3.39.

EXAMPLE 8 A. Preparation ofL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine

To a stirred solution of 3.0 g. (0.0126 mole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate in 20 ml. of 2 Nsodium hydroxide solution maintained at 0° C. under a nitrogenatmosphere is added a solution of 3 ml. of carbobenzyloxy chloride in 10ml. of diethyl ether. After stirring at 0° C. for one hour, followed byone hour at 25° C., the reaction mixture is extracted with 50 ml. ofdiethyl ether. The aqueous portion is acidified to pH 3-4 with a 6 Nhydrochloric acid solution and the crude product is extracted into 100ml. of ethyl acetate and washed three times with 25 ml. of water. Afterdrying over anhydrous magnesium sulfate and filtering, solvent isremoved under reduced pressure to give 1.5 g. (34.5%) ofL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine as a viscousoil.

B. Preparation of pivaloyloxymethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A mixture of 2.1 g. (6.1 mmole) ofL-N-carbenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine, 0.93 g. (6.2mmole) of chloromethylpivalate, 0.63 g. (6.3 mmole) of potassiumbicarbonate and 0.15 g. potassium iodide in 60 ml. of acetone and 4 ml.of water is stirred at reflux under nitrogen for 18 hours. Afterconcentrating under reduced pressure, 50 ml. of water is added and theN-carbobenzyloxy derivative of the desired ester is extracted with three50 ml. portions of diethyl ether. The ether extract is washed with 50ml. of water, dried over anhydrous magnesium sulfate and concentratedunder reduced pressure. The oily residue is dissolved in 100 ml. ofabsolute ethanol and 4 ml. of a 9.6 N ethanolic-anhydrous hydrogenchloride solution and hydrogenated with 1 g. of a 10%palladium-on-carbon catalyst at an initial pressure of 39 p.s.i. for 24hours. After removing catalyst by filtration, the filtrate isconcentrated under reduced pressure. The residue is dissolved in 5 ml.of water, made basic to pH 8 with a saturated sodium carbonate solutionand the insoluble product extracted into 25 ml. of ethyl acetate. Afterdrying over anhydrous magnesium sulfate and filtering, 1 ml. of 9.6 Nethanolic-anhydrous hydrogen chloride solution is added and the solutionis concentrated under reduced pressure to give 0.50 g. (22.6%) of thehydrochloride of pivaloyloxymethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride, Rf = 0.86upon thin layer chromatography [fluorescent silica gel plate developedwith a 5:2:3 (by volume) mixture of n-butanol:acetic acid-water].

Anal. calcd. for C₁₆ H₂₃ NO₆.HCl: C, 53.11; H, 6.69; N, 3.87. Found: C,53.76; H, 6.64; N, 3.69.

EXAMPLE 9 A. Preparation of 1,2-ethylene bisL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate

A solution of 7.8 g. (0.023 mole) ofL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine, 1.88 g.(0.01 mole) of 1,2-dibromoethane and 2.1 g. (0.021 mole) oftriethylamine in 20 ml. dimethylformamide is heated at 85°-90° C. for 10hours and then poured into 200 ml. water. The blocked bis ester isextracted with three 100 ml. portions of ethyl acetate and washed with100 ml. of a saturated sodium bicarbonate solution and 100 ml. of asaturated sodium chloride solution. After drying over anhydrousmagnesium sulfate and concentrating under reduced pressure at 30°-40°C., 5.3 g. (74%) of 1,2-ethylene bisL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate isobtained.

B. Preparation of 1,2-ethylene bisL-3-(3,4-dihydroxyphenyl)-2-methylalaninate dihydrochloride

A solution of 5.0 g. (6.98 mmole) of 1,2-ethylene bisL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate in 120 ml.of a 25% methanol-75% ethyl acetate (by volume) mixture is hydrogenatedat an initial pressure of 35 p.s.i. with 2 g. of 10% palladium-on-carboncatalyst until hydrogen uptake is complete. After filtering to removecatalyst, solvents are removed under reduced pressure. The residue isdissolved in a 10% ethanol-90% ethyl acetate (by volume) mixture,stirred with 5 ml. of a saturated sodium carbonate solution and 5 g. ofsolid sodium carbonate. Anhydrous magnesium sulfate is added, themixture is filtered and the filtrate acidified with 1 ml. of 9.6 Nethanolic-anhydrous hydrogen chloride solution. Solvents are removedunder reduced pressure at a temperature of 20° to 30° C. to give1,2-ethylene bis L-3-(3,4-dihydroxyphenyl)-2-methylalaninatedihydrochloride as the ethyl acetate solvate.

Anal. calcd. for C₂₂ H₂₈ N₂ O₈.2HCl.2C₄ H₈ O₂ : C, 51.65; H, 6.65; N,4.07. Found: C, 50.91; H, 6.69; N, 4.27.

EXAMPLE 10 Preparation of 1,3-propylene bisL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate

A solution of 7.8 g. (0.023 mole) ofL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate, 2.1 g.(0.020 mole) of triethylamine and 2.02 g. (0.010 mole) of1,3-dibromopropane in 20 ml. dimethylformamide is heated under nitrogenfor 15 hours at 95° C. and then poured into 200 ml. of water. Theproduct is extracted with three 100 ml. portions of ethyl acetate andwashed with 50 ml. of a dilute sodium bicarbonate solution (5%), 50 ml.of water and finally 50 ml. of a saturated solution of sodium chloride.After drying over anhydrous magnesium sulfate and concentrating underreduced pressure, 5.4 g. (73.8%) of 1,3-propylene bisL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate isobtained.

B. Preparation of 1,3-propylene bisL-3-(3,4-dihydroxyphenyl)-2-methylalaninate dihydrochloride

A solution of 5.4 g. (7.39 mmole) of 1,3-propylene bisL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate in 100 ml.25% ethanol-75% ethyl acetate (by volume) is hydrogenated at an initialpressure of 35 p.s.i. with 2.5 g. of a 10% palladium-on-carbon catalystat 25° C. until hydrogen uptake ceases. After removing catalyst byfiltration, solvents are removed under reduced pressure. The residue isdissolved in 10% methanol-90% ethyl acetate (by volume), stirred with 5ml. of a saturated sodium carbonate solution and 5 g. of solid sodiumcarbonate. Five grams of anhydrous magnesium sulfate is added, themixture is filtered and the filtrate acidified with 1 ml. of 9.6 Nethanolic-anhydrous hydrogen chloride solution. The solution isconcentrated under reduced pressure to about 50 - 60 ml. volume anddecanted from an insoluble gum. The gum is stirred with 25 ml. of ethylacetate, filtered and dried to give 1.74 g. (33%) of 1,3-propylene bisL-3-(3,4-dihydroxyphenyl)-2-methylalaninate dihydrochloride as the ethylacetate solvate, Rf = 0.56, thin layer chromatography [fluorescentsilica gel plate developed with a solution containing equal parts (byvolume) of n-butanol, acetone, acetic acid, water and benzene].

EXAMPLE 11 A. Preparation of 1-chloro-1-succinimidopropane

Anhydrous hydrogen chloride is bubbled through a mixture of 10 g. (0.072mole) of N-propenylsuccinimide and 1.04 g. of stannic chloride for 6hours. The solution is allowed to stand at room temperature for 10 days,the solution being saturated again with hydrogen chloride gas after 3days and 4 days. Solvents are removed under reduced pressure at 30°-40°C. to give 1-chloro-1-succinimidopropane as a yellow oil.

B. Preparation of α-succinimidopropylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.2 g. (0.020 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-3-methylalanine,2.1 g. (0.021 mole) of triethylamine and 3.51 g. (0.020 mole) of1-chloro-1-succinimidopropane in 20 ml. dimethylformamide is heated at90° C. for 10 hours and then poured into 200 ml. water. The product isextracted with three 100 ml. portions of ethyl ether and washed with 50ml. of 5% sodium hydroxide, 50 ml. of water and 50 ml. of a saturatedsolution of sodium chloride. After drying over anhydrous magnesiumsulfate and filtering, solvents are removed under reduced pressure togive 8.6 g. (68%) of α-succinimidopropylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate,Rf = 0.2, thin layer chromatography [fluorescent silica gel platedeveloped with chloroform].

C. Preparation of α-succinimidopropylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 8.6 g. (0.014 mole) of α-succinimidopropylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 120 ml. of a 25% ethanol-75% ethyl acetate (by volume) solution ishydrogenated with 4 g. of a 10% palladium-on-carbon catalyst at aninitial pressure of 40 p.s.i. for 18 hours until hydrogen uptake ceases.After removing catalyst by filtration, solvents are removed underreduced pressure at 30°-40° C. The residue is dissolved in 10%ethanol-90% ethyl acetate (by volume) and stirred with 5 ml. ofsaturated sodium carbonate solution and excess solid sodium carbonatefor 2 minutes. Ten grams of anhydrous magnesium sulfate is added, themixture is filtered and the filtrate acidified with 2 ml. of 9.6 Nethanolic-hydrogen chloride solution. The solution is concentrated todryness under reduced pressure, 100 ml. ethyl acetate is added and themixture concentrated again to dryness under reduced pressure. Ethylacetate, 100 ml., is added and after stirring at 25° C. for 1 hour, theproduct is removed by filtration and dried under reduced pressure togive 3.0 g. (51.0%) of α-succinimidopropylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride as the ethanolsolvate, Rf = 0.63, thin layer chromatography [fluorescent silica gelplate developed with 30% methanol-70% benzene (by volume)].

Anal. calcd. for C₁₇ H₂₂ N₂ O₆.HCl.C₂ H₅ OH: C, 52.71; H, 6.75; N, 6.47.Found: C, 53.62; H, 6.51; N, 6.32.

EXAMPLE 12 A. Preparation of N-chloromethylglutarimide

Thionyl chloride, 8.35 g. (0.070 mole) is added slowly to a solution of9.0 g. (0.063 mole) of N-hydroxymethylglutarimide in 50 ml. benzene at40° C. After addition is complete, the solution is stirred at reflux for1.5 hours and then at room temperature for an additional 1.5 hours.Benzene is removed under reduced pressure at 30°-40° C. and the residueis distilled to give 5.4 g. (53%) of N-chloromethylglutarimide, b.p.97°-100° C. at 0.1 mm.

B. Preparation of glutarimidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.2 g. (0.020 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,2.02 g. (0.020 mole) of triethylamine and 3.23 g. (0.020 mole) ofN-chloromethylglutarimide in 20 ml. dimethylformamide is stirred at 70°C. for 5 hours, then at 20°-30° C. for 5 hours and finally poured into200 ml. of water. The product is extracted with three 100 ml. portionsof ethyl acetate, washed with 50 ml. of a 5% sodium hydroxide solution,50 ml. of water and 50 ml. of saturated sodium chloride solution anddried over anhydrous magnesium sulfate. After filtering, solvents areremoved under reduced pressure to give 12.1 g. (95%) ofglutarimidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate,Rf = 0.14 upon thin layer chromatography [fluorescent silica gel platedeveloped with chloroform].

C. Preparation of glutarimidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 12 g. (0.0189 mole) of glutarimidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 130 ml. of 25% absolute ethanol-75% ethyl acetate (by volume) ishydrogenated with 5 g. of a 10% palladium-on-carbon catalyst at 20°-25°C. and an initial pressure of 40 p.s.i. for 18 hours until hydrogenuptake ceases. After removing catalyst by filtration and concentratingto dryness under reduced pressure, the residue is dissolved in 200 ml.of a 10% absolute ethanol-90% ethyl acetate (by volume) solution andstirred with 5 ml. of a saturated sodium carbonate solution and excesssolid carbonate for 2 minutes. Ten grams of anhydrous magnesium sulfateis added and after a few minutes is removed by filtration. Solvents areremoved under reduced pressure, the residue is washed with 25 ml. ofhexane and then 25 ml. of ethyl acetate and dried under reducedpressure. The residue is retreated with sodium carbonate as before toremove the last traces of α-methyl-3,4-dihydroxyphenylalanine andconverted to the hydrochloride salt with 3 ml. of 9.6 Nethanolic-anhydrous hydrogen chloride to give 3.0 g. (36%) ofglutarimidomethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride as the ethyl acetate solvate, homogeneous upon thin layerchromatography [fluorescent silica gel plate developed with 30%methanol-70% benzene (by volume)], Rf = 0.56.

Anal. calcd. for C₁₆ H₂₀ N₂ O₆.HCl.3/4C₄ H₈ O₂ : C, 51.99; H, 6.20; N,6.38. Found: C, 52.15; H, 6.45; N, 6.53.

EXAMPLE 13 A. Preparation of2-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanyloxymethyl]-1,2-benzisothiazol-3(2H)-one-1,1-dioxide

A solution of 7.65 g. (0.015 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,1.5 g. (0.015 mole) triethylamine and 3.0 g. (0.015 mole) ofN-chloromethylsaccharin in 15 ml. dimethylformamide is heated at 75°-80°C. for 17 hours and then poured into 150 ml. water. The product isextracted with three 100 ml. portions of ethyl acetate, washed with 50ml. of a saturated sodium bicarbonate solution, 50 ml. of water and 50ml. of a saturated sodium chloride solution and is dried over anhydrousmagnesium sulfate. After filtering, solvents are removed under reducedpressure to give 9.3 g. (100%) of2-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanyloxymethyl]-1,2-benzisothiazol-3(2H)-one-1,1-dioxide,Rf = 0.32, thin layer chromatography [fluorescent silica gel platedeveloped with chloroform].

B. Preparation of2-[L-3-(3,4-dihydroxyphenyl)-2-methylalanyloxymethyl]-1,2-benzisothiazol-3(2H)-one-1,1-dioxidehydrochloride

A solution of 3.0 g. (0.0043 mole) of the2-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanyloxymethyl]-1,2-benzisothiazol-3(2H)-one-1,1-dioxidein 100 ml. absolute ethanol and 5 ml. of 8 N ethanolic -anhydroushydrogen chloride solution is hydrogenated with 1.5 g. of a 10%palladium-on-carbon catalyst at 20°-25° C. and an initial pressure of 35p.s.i. for 20 hours until hydrogen uptake ceases. After removingcatalyst by filtration and concentrating to dryness under reducedpressure, the residue is stirred with 50 ml. of ethyl acetate for 1 hourand the ethyl acetate decanted off. The residue is dissolved in 200 ml.of 20% ethanol - 80% ethyl acetate (by volume) and stirred with 10 ml.saturated sodium carbonate solution and excess solid sodium carbonate.Ten grams anhydrous magnesium sulfate is added and after a few minutesis removed by filtration and the filtrate acidified with 1 ml. of 9.6 Nethanolic - anhydrous hydrogen chloride solution. Solvents are removedunder reduced pressure to give 0.2 g. (10.0%) of2-[L-3-(3,4-dihydroxyphenyl)-2-methylalanyloxymethyl]-1,2-benzisothiazol-3(2H)-one-1,1-dioxidehydrochloride as the ethyl acetate solvate, Rf = 0.74, thin layerchromatography [fluorescent silica gel plate developed with a solventconsisting of equal parts (by volume) of benzene, water, acetic acid,n-butanol and acetone.]

Anal. calcd. for C₁₈ H₁₈ N₂ O₇ S.HCl.1/4 C₄ H₈ O₂ : C, 49.08; H, 4.55;N, 6.03. Found: C, 49.27; H, 4.76; N, 5.65.

EXAMPLE 14 A. Preparation of1-methyl-2-[L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanyloxymethyl]-imidazole

A solution of 7.8 g. (0.0226 mole) ofL-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine, 4.2 g.(0.042 mole) triethylamine and 3.34 g. (0.0256 mole) of1-methyl-2-chloromethylimidazole in 20 ml. dimethylformamide is heatedat 70°-75° C. for 10 hours and then poured into 200 ml. water. Theproduct is extracted with three 100 ml. portions of ethyl acetate,washed with 50 ml. of a saturated sodium bicarbonate solution, 50 ml. ofa saturated sodium chloride solution and concentrated under reducedpressure to give 2.2 g. (22%) of1-methyl-2-[L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanyloxymethyl]-imidazole,homogeneous upon thin layer chromatography [fluorescent silica gel platedeveloped with 15% methanol-85% chloroform (by volume)] Rf = 0.66.

B. Preparation ofL-1-methyl-2-[2-(3,4-dihydroxybenzyl)alanyloxymethyl]-imidazoledihydrochloride dihydrate

A solution of 2.1 g. (4.78 mmole) of1-methyl-2-[L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanyloxymethyl]-imidazolein 100 ml. absolute ethanol is hydrogenated with 1 g. of a 10%palladium-on-carbon catalyst at an initial pressure of 35 p.s.i. for 4hours. After removing catalyst by filtration and concentrating to 50 ml.under reduced pressure, 2 ml. of 9.6 N ethanolic-anhydrous hydrogenchloride is added and the remainder of solvents are removed underreduced pressure. The residue is stirred with 200 ml. 20% ethanol-80%ethyl acetate (by volume), 10 ml. of saturated sodium carbonate solutionand excess solid sodium carbonate. Ten grams of anhydrous magnesiumsulfate is added and after a few minutes is removed by filtration. Thefiltrate is acidified with 1 ml. of 9.6 N ethanolic-anhydrous hydrogenchloride solution. Solvents are removed under reduced pressure to give0.2 g. (8.5%) ofL-1-methyl-2-[2-(3,4-dihydroxybenzyl)-alanyloxymethyl]-imidazoledihydrochloride dihydrate as the ethyl acetate solvate, Rf = 0.3 uponthin layer chromatography [fluorescent silica gel plate developed with asolution consisting of equal parts (by volume) of n-butanol, aceticacid, water, benzene and acetone.]

Anal. calcd. for C₁₈ H₁₉ N₃ O₄.2HCl.2H₂ O.1/2C₄ H₈ O₂ : C, 44.55; H,6.34; N, 9.17. Found: C, 44.62; H, 6.84; N, 8.95.

EXAMPLE 15 A. Preparation of 1-methyl-3-chloromethylhydantoin

Thionyl chloride, 30 ml., is added slowly over 20 minutes to a wellstirred mixture of 25 g. (0.173 mole) of1-methyl-3-hydroxymethylhydantoin and 160 ml. benzene at reflux. Afterstirring at reflux for 2 hours, the reaction mixture is concentrated todryness under reduced pressure, 70 ml. of benzene is added and thesolution concentrated again to dryness. After repeating this process onemore time with 70 ml. benzene, the residue is extracted with three 100ml. portions of carbon tetrachloride. Removal of solvents under reducedpressure gives 15.7 g. (55.7%) of the 1-methyl-3-chloromethylhydantoin.

B. Preparation of1-methyl-3-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanyloxymethyl]-hydantoin

A solution of 10.2 g. (0.020 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,2.1 g. (0.021 mole) of triethylamine and 3.25 g. (0.020 mole) of1-methyl-3-chloromethylhydantoin in 23 ml. dimethylformamide is heatedat 70° C. for 18 hours and then poured into 230 ml. water. The productis extracted with three 100 ml. portions of ethyl acetate, washed with50 ml. of dilute sodium hydroxide solution (5%), 50 ml. of water and 50ml. of a saturated sodium chloride solution and dried over anhydrousmagnesium sulfate. After filtering, solvents are removed under reducedpressure to give 11.7 g. (92%) of1-methyl-3-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanyloxymethyl]-hydantoin.

C. Preparation ofL-1-methyl-3-[2-(3,4-dihydroxybenzyl)alanyloxymethyl]-hydantoinhydrochloride hydrate

A solution of 4.0 g. (6.3 mmole) of1-methyl-3-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanyloxymethyl]-hydantoinin 140 ml. absolute ethanol and 2 g. of a 10% palladium-on-carboncatalyst is hydrogenated at an initial pressure of 36 p.s.i. for 20hours. After removing catalyst by filtration and concentrating todryness under reduced pressure, the residue is washed with 100 ml.hexane. The hexane insoluble material is dissolved in 150 ml. of 10%methanol-90% ethyl acetate (by volume), stirred with 5 ml. of saturatedsodium carbonate solution and excess sodium carbonate and dried overanhydrous magnesium sulfate. After filtering, the filtrate is acidifiedwith 2 ml. of 9.6 N ethanolic-anhydrous hydrogen chloride andconcentrated to dryness under reduced pressure. The residue is stirredwith 80 ml. ethyl acetate for 3 hours, filtered and dried under reducedpressure to give 0.50 g. (18%) ofL-1-methyl-3-[2-(3,4-dihydroxybenzyl)-alanyloxymethyl]-hydantoinhydrochloride hydrate as the ethyl acetate solvate.

Anal. calcd. for C₁₅ H₁₉ N₃ O₆.HCl.H₂ O.1/2C₄ H₈ O₂ : C, 46.84; H, 6.01;N, 9.64. Found: C, 46.28; H, 6.09; N, 9.06.

EXAMPLE 16 A. Preparation of 2-phenoxyethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 4.5 g. (0.0088 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,0.90 g. (0.009 mole) of triethylamine and 1.81 g. (0.009 mole) of2-bromoethylphenylether in 15 ml. of dimethylformamide is heated at70°-75° C. for 24 hours, then cooled and poured in 150 ml. of water. Theproduct is extracted with three 100 ml. portions of ethyl ether, washedwith 50 ml. of a 5% sodium hydroxide solution, 50 ml. of water and 50ml. of a saturated sodium chloride solution and dried over anhydrousmagnesium sulfate. After filtering, solvents are removed under reducedpressure to give 4.8 g. (86.5%) of 2-phenoxyethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate,homogeneous upon thin layer chromatography [fluorescent silica gel platedeveloped with chloroform] Rf = 0.91.

B. Preparation of 2-phenoxyethyl L-3-(3,4-dihydroxybenzyl)alaninatehydrochloride hemihydrate

A solution of 4.7 g. (7.5 mmole) of 2-phenoxyethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 120 ml. of absolute ethanol is hydrogenated with 1.7 g. of a 10%palladium-on-carbon catalyst at an initial pressure of 20 p.s.i. for 20hours. After filtering off catalyst, solvents are removed under reducedpressure and the residue is chromatographed on a column of 75 g. silicagel. Elution with 400 ml. of a 5% methanol-95% benzene (by volume)mixture gives 1.42 g. (58%) of ester base, m.p. 35°-42° C. homogeneousupon thin layer chromatography [fluorescent silica gel plate developedwith 30% methanol-70% benzene (by volume)] Rf = 0.52. The base isconverted to the hydrochloride salt by dissolving in 25 ml. of a 50%chloroform-50% methanol (by volume) mixture and acidifying with 2 ml. of9.6 N ethanolic-anhydrous hydrogen chloride solution. Solvents areremoved under reduced pressure to give 2-phenoxyethylL-3-(3,4-dihydroxybenzyl)-alaninate hydrochloride hemihydrate.

Anal. calcd. for C₁₈ H₂₁ NO₅.HCl.1/2H₂ O: C, 57.37; H, 6.15; N, 3.72.Found: C, 57.17; H, 6.16; N, 3.41.

EXAMPLE 17 A. Preparation of 2-succinimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 4.5 g. (8.8 mmole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,0.90 g. (9 mmole) of triethylamine and 1.85 g. (9.3 mmole) ofN-(2-bromoethyl)-succinimide in 15 ml. of dimethylformamide is heated at95° C. for 19 hours, then cooled and poured into 150 ml. water. Theproduct is extracted with three 100 ml. portions of ethyl ether, washedwith 50 ml. of a 5% sodium hydroxide solution, 50 ml. of water and 50ml. of a saturated sodium chloride solution and dried over anhydrousmagnesium sulfate. After filtering, solvents are removed under reducedpressure to give 4.8 g. (86%) of 2-succinimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate,homogeneous upon thin layer chromatography [fluorescent silica gel platedeveloped with chloroform] Rf = 0.27.

B. Preparation of 2-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hemihydrate

A suspension of 2.5 g. (3.94 mmole) of 2-succinimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 75 ml. methanol, 75 ml. ethanol and 3 ml. of a 7.6 Nethanolic-anhydrous hydrogen chloride solution is hydrogenated with 1.2g. of a 10% palladium-on-carbon catalyst at an initial pressure of 20p.s.i. for 20 hours. After removing catalyst by filtration, solvents areremoved under reduced pressure and the residue is stirred with 25 ml. ofbenzene and then 25 ml. of ethyl acetate. The insoluble material istreated with 100 ml. of 10% ethanol-90% ethyl acetate (by volume), 5 ml.of a saturated sodium carbonate solution and 5 g. solid sodiumcarbonate. The organic extract is dried over anhydrous magnesiumsulfate, then filtered and concentrated under reduced pressure. One ml.of 9.6 N ethanolic- anhydrous hydrogen chloride solution is added.Removal of all solvents under reduced pressure gives 0.5 g. (33%) of the2-succinimidoethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride hemihydrate, homogeneous upon thin layer chromatography[fluorescent silica gel plate developed with 30 % methanol-70% benzene(by volume)], Rf = 0.4.

Anal. calcd. for C₁₆ H₂₀ N₂ O₆.HCl.1/2H₂ O: C, 50.33; H, 5.54; N, 7.34.Found: C, 50.89; H, 5.65; N, 7.22.

EXAMPLE 18 A. Preparation of 1,2-ethylene bis[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate]

A solution of 10.18 g. (0.020 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,2.12 g. (0.021 mole) triethylamine and 0.99 g. (0.010 mole) of1,2-dichloroethane in 35 ml. dimethylformamide is stirred under nitrogenat 105°-110° C. for 28 hours and then poured into 400 ml. ice water. Theproduct is extracted into 800 ml. ethyl ether, washed with 100 ml. of a5% sodium hydroxide solution, 100 ml. of water, dried over anhydrousmagnesium sulfate, filtered and concentrated under reduced pressure. Theresidue is chromatographed on 800 g. silica gel, 2.25 g. (21.5%) of1,2-ethylene bis[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate]eluted with chloroform.

B. Preparation ofL,L-2-[2-(3,4-diphenylmethylenedioxybenzyl)-alanyloxy]-ethyl2-(3,4-dihydroxybenzyl)-alaninate bishydrogen oxalate

A solution of 2.25 g. (2.2 mmole) of 1,2-ethylene bis[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate]in 100 ml. absolute ethanol is hydrogenated with 1.2 g. of 10%palladium-on-carbon catalyst at an initial pressure of 30 p.s.i. for 28hours until hydrogen uptake is complete. After removing catalyst byfiltration, solvents are removed under reduced pressure. The residue isstirred with 100 ml. of 10% ethanol-90% ethyl acetate (by volume), 2 ml.of saturated sodium carbonate solution and 3 g. of solid sodiumcarbonate for 15 minutes and then filtered. The filtrate is dried overanhydrous magnesium sulfate, filtered and concentrated under reducedpressure. The residue is chromatographed over silica gel and eluted with30% methanol-70% benzene (by volume) to give 220 mg. of product. Thisproduct is converted to the oxalate salt with 500 mg. of oxalic acid in10 ml. of ethanol by precipitation with sufficient ethyl ether. Afterone more precipitation from 10 ml. of ethanol by adding sufficient ethylether, 246 mg. (14%) of L,L-2-[2-(3,4-diphenylmethylenedioxybenzyl)-alanyloxy]-ethyl2-(3,4-dihydroxybenzyl)-alaninate bishydrogen oxalate is obtained.

Anal. calcd. for C₃₅ H₃₆ N₂ O₂.2C₂ H₂ O₄ : C, 59.08; H, 5.08; N, 3.53.Found: C, 59.15; H, 5.18; N, 3.55.

EXAMPLE 19 A. Preparation of 2-phthalimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.18 g. (0.020 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate,2.12 g. (0.021 mole) triethylamine and 5.08 g. (0.020 mole) ofN-(2-bromoethyl)-phthalimide in 30 ml. dimethylformamide is stirredunder nitrogen at 105°-110° C. overnight and then poured into 600 ml.ice water. The product is extracted into three 100 ml. portions of ethylether and washed with 50 ml. of water. The ether extract is dried overanhydrous magnesium sulfate, filtered and concentrated under reducedpressure to give a gummy solid. Chromatography over silica gel andelution with chloroform gives 10.88 g. (80%) of 2-phthalimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate,Rf = 0.53, thin layer chromatography [fluorescent silica gel platedeveloped with chloroform].

B. Preparation of 2-phthalimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 10.88 g. (0.0159 mole) of 2-phthalimidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 125 ml. ethyl acetate is hydrogenated with 6 g. of a 10%palladium-on-carbon catalyst at an initial pressure of 31 p.s.i.for 5hours until hydrogen uptake ceases. After removing catalyst byfiltration and removing solvents under reduced pressure, the residue isdissolved in 150 ml. absolute ethanol containing 4 ml. of 5.15 Nethanolic-anhydrous hydrogen chloride solution and hydrogenated with 4.3g. of palladium-on-carbon catalyst at 27-38 p.s.i. for 5 days.Additional 4.3 g. amounts of 10% palladium-on-carbon catalyst are addedduring this time. After removing catalyst by filtration, andconcentrating under reduced pressure, the residue is washed with 100 ml.of petroleum ether and dissolved in ethanol. It is precipitated threetimes from ethanol by adding sufficient ethyl ether to precipitate theproduct. The product is dried under reduced pressure to give 2.80 g.(41.8%) of 2-phthalimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride, m.p.138.0°-140.0° C. dec., homogeneous upon thin layer chromatography[fluorescent silica gel plate developed with 50% methanol-50% benzene(by volume)] Rf = 0.61.

Anal. calcd. for C₂₀ H₂₀ N₂ O₆.HCl: C, 57.07; H, 5.03; N, 6.65; Cl,8.42. Found: C, 56.31; H, 5.62; N, 6.48; Cl, 8.75.

EXAMPLE 20 A. Preparation of 2-acetoxyethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.0 g. (0.0196 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,2.39 g. (0.0235 mole) triethylamine and 2.40 g. (0.0196 mole) of2-chloroethyl acetate in 30 ml. dimethylformamide is stirred undernitrogen at 110° C. for 20 hours and then poured into 500 ml. ice water.The product is extracted into four 200 ml. portions of ethyl ether whichare combined and washed with 200 ml. of water, 200 ml. of a 5% sodiumhydroxide solution and then 200 ml. of water. After drying overanhydrous magnesium sulfate and filtering, solvents are removed underreduced pressure. The residue is chromatographed on 700 g. silica gel.Elution with 5% methanol-95% chloroform (by volume) gives 5.60 g. (48%)of 2-acetoxyethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate.

B. Preparation of 2-acetoxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate

A solution of 5.60 g. (0.0094 mole) of 2-acetoxyethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methalaninatein 100 ml. absolute ethanol is hydrogenated with 2.8 g. of a 10%palladium-on-carbon catalyst at an initial pressure of 37 p.s.i. for 24hours until hydrogen uptake is complete. After removing catalyst byfiltration and removing solvents under reduced pressure, the residue iswashed with 100 ml. of petroleum ether and dissolved in 124 ml. of 10%ethanol-90% ethyl acetate (by volume). Sodium carbonate, 6.2 g., and 4ml. of a saturated sodium carbonate solution are added and stirred for20 minutes. The mixture is filtered, dried over anhydrous magnesiumsulfate, filtered again and concentrated under reduced pressure. Theresidue is chromatographed on silica gel and eluted with 20%methanol-80% benzene (by volume). Recrystallization is accomplished bydissolving it in ethyl acetate and adding sufficient cyclohexane toprecipitate it to give 1.01 g. (36%) of 2-acetoxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate, m.p. 114°-118° C. dec.

Anal. Calcd. for C₁₄ H₁₉ NO₆ : C, 56.55; H, 6.44; N, 4.71. Found: C,56.64; H, 6.63; N, 4.33.

EXAMPLE 21 A. Preparation of 2-benzamidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.0 g. (0.0196 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,2.11 g. (0.021 mole) triethylamine and 3.64 g. (0.0196 mole) ofN-(2-chloroethyl)-benzamide in 20 ml. dimethylformamide is stirred undernitrogen at 110° C. for 20 hours and then poured into 400 ml. ice water.The precipitate is removed by filtration, washed with 100 ml. of waterand dissolved in 200 ml. of ethyl ether. The ether solution is washedwith 50 ml. of a 5% sodium hydroxide solution, 50 ml. of water and driedover anhydrous magnesium sulfate. Drying agent is filtered off and thefiltrate concentrated under reduced pressure to give 11.21 g. (87%) of2-benzamidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate,Rf = 0.7, thin layer chromatography [fluorescent silica gel platedeveloped with 5% methanol-95% chloroform (by volume)].

B. Preparation of 2-benzamidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate oxalate hemihydrate

A solution of 11.21 g. (0.017 mole) of 2-benzamidoethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 100 ml. absolute ethanol is hydrogenated with 5.5 g. of 10%palladium-on-carbon catalyst at an initial pressure of 30 p.s.i. for 7hours. After removing catalyst by filtration and removing solvents underreduced pressure, the residue is stirred with 100 ml. petroleum etherovernight. The insoluble material is dissolved in 250 ml. of 10%ethanol-90% ethyl acetate (by volume), shaken for 10 minutes with 12 ml.saturated sodium carbonate solution and 12 g. sodium carbonate andfiltered. The filtrate is dried over anhydrous magnesium sulfate,filtered and concentrated under reduced pressure. The residue is treatedwith 1.3 g. of oxalic acid dissolved in 25 ml. of absolute ethanol, theoxalate salt being precipitated by addition of sufficient ethyl ether.Two more precipitations are carried out by dissolving the product inethanol and adding sufficient ethyl ether to precipitate the product togive 1.60 g. (23 %) of 2-benzamidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate oxalate hemihydrate,homogeneous upon thin layer chromatography [fluorescent silica gel platedeveloped with 50% methanol-50% chloroform (by volume)] Rf = 0.44.

Anal. calcd. for C₁₉ H₂₂ N₂ O₅.1/2C₂ H₂ O₄.1/2H₂ O: C, 58.24; H, 5.86;N, 6.79. Found: C, 58.39; H, 5.73; N, 6.37.

EXAMPLE 22 A. Preparation of naphthalimidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.2 g. (0.020 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,2.02 g. (0.020 mole) of triethylamine and 4.9 g. (0.020 mole) ofN-chloromethylnaphthalimide in 50 ml. dimethylformamide is stirred at90° C. for 20 hours, then poured into 500 ml. ice water. The product isextracted into 200 ml. of ethyl acetate, washed with 50 ml. of a 5%sodium hydroxide solution, 50 ml. of water and 50 ml. of saturatedsodium chloride solution and dried over anhydrous magnesium sulfate.After filtering, solvents are removed under reduced pressure to give13.1 g. (91%) of naphthalimidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate.

B. Preparation of naphthalimidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 13 g. (0.0181 mole) of naphthalimidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 150 ml. of 25% absolute ethanol-75% ethyl acetate (by volume) ishydrogenated with 5 g. of a 10% palladium-on-carbon catalyst at 25° C.and an initial pressure of 40 p.s.i. for 24 hours until hydrogen uptakeis complete. After removing catalyst by filtration and concentrating thefiltrate under reduced pressure, the residue is dissolved in 200 ml. of10% absolute ethanol-90% ethyl acetate (by volume) and stirred with 5ml. of saturated sodium carbonate solution and 5 g. of solid sodiumcarbonate for 10 minutes. The mixture is filtered, the filtrate driedwith anhydrous magnesium sulfate, filtered again and concentrated underreduced pressure. The residue is washed with 100 ml. of hexane to removediphenylmethane, dissolved in 25 ml. of absolute ethanol and acidifiedwith 5 ml. of 8 N ethanolic-anhydrous hydrogen chloride solution.Addition of ethyl ether precipitates the hydrochloride salt of thenaphthalimidomethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninate.

EXAMPLE 23 A. Preparation of racemicN-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine

To a stirred solution of 8.0 g. (0.0378 mole) of racemicDL-3-(3,4-dihydroxyphenyl)-2-methylalanine in 60 ml. of 2 N sodiumhydroxide solution under nitrogen is added a solution of 9 ml. ofcarbobenzyloxy chloride in 25 ml. diethyl ether. After stirring at 0° C.for one hour, followed by one hour at 25° C., the reaction mixture isextracted with 50 ml. of diethyl ether. The aqueous portion is acidifiedto pH 3 with 6 N hydrochloric acid and the crude product is extractedinto 100 ml. of ethyl acetate and washed three times with 35 ml. ofwater. After drying over anhydrous magnesium sulfate and filtering,solvent is removed under reduced pressure to give 4.5 g. (34%) of theracemic N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine as aviscous oil.

B. Preparation of racemic pivaloyloxymethyl3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 4.2 g. (0.012 mole) of racemicN-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine, 1.3 g. (0.013mole) of triethylamine and 1.26 g. (0.013 mole) of chloromethylpivalatein 20 ml. dimethylformamide is stirred at 90° C. for 20 hours and thenpoured into 200 ml. water. The product is extracted into 100 ml. ofethyl acetate and washed with 25 ml. of a saturated sodium bicarbonatesolution and 25 ml. of water. After drying over anhydrous magnesiumsulfate and filtering, the filtrate is concentrated under reducedpressure to give the N-carbobenzyloxy derivative of the desired ester.This material is dissolved in 100 ml. of absolute ethanol containing 10ml. of a 9.6 N ethanolic-anhydrous hydrogen chloride solution andhydrogenated with 3 g. of a 10% palladium-on-carbon catalyst at aninitial pressure of 35 p.s.i. for 24 hours. After removing catalyst byfiltration, the filtrate is concentrated under reduced pressure. Theresidue is dissolved in 25 ml. of water, made basic with a saturatedsodium carbonate solution to pH 8 and the insoluble product extractedwith 100 ml. of ethyl acetate. After drying over anhydrous magnesiumsulfate and filtering, 5 ml. of 9.6 N ethanolic anhydrous hydrogenchloride solution is added and the solution concentrated under reducedpressure to give 1.5 g. (22.6%) of the hydrochloride of the racemicpivaloyloxymethyl 3-(3,4-dihydroxyphenyl)-2-methylalaninate, homogeneousupon thin layer chromatography [fluorescent silica gel plate developedwith a 5-2-3 (by volume) mixture of n-butanolacetic acid-water] Rf =0.86.

EXAMPLE 24 Preparation of 2-acetamidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A slurry of 88.3 g. (0.30 mole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine hydrochloride ethanol solvate(by concentration of an ethanolic solution of the hydrochloride underreduced pressure) and 146.4 g. (1.42 mole) of N-acetylethanolamine,under nitrogen, is warmed to 104°-108° C. Thionyl chloride, 84.8 g.(0.713 mole) is added over 15 minutes with stirring. The reactionmixture foams vigorously during the addition. After addition iscomplete, the reaction mixture is stirred at 104°-108° C. for 18 hours.Additional thionyl chloride, 42.4 g. (0.357 mole) is added over sevenminutes. The reaction mixture is allowed to stir at 104°-108° C. foranother 31/2 hours, then cooled to 30° C. and concentrated under reducedpressure to yield a viscous oil. This oil is slurried with 100 ml. ofchloroform and the chloroform removed under reduced pressure. This isrepeated three more times and then the oil is washed with 100 ml. ofbenzene which is decanted. The residue is dissolved in 700 ml. ofisopropanol and added to 6 l. of ethyl ether. The precipitate whichforms is washed with 500 ml. of ethyl ether and shaken with 6 l. of 10%ethanol-90% ethyl acetate (by volume), 150 ml. of saturated sodiumcarbonate solution and 100 g. of sodium carbonate. The organic extractis dried over anhydrous magnesium sulfate, filtered and concentratedunder reduced pressure to give the free base of the acetamidoethylester. This base is treated with 15 g. of fumaric acid in 300 ml. ofisopropanol and the fumarate salt precipitated by adding sufficientethyl ether. The fumarate salt is precipitated once more fromisopropanol by adding sufficient ethyl ether and then converted back tothe free base as before by shaking with 200 ml. of 10% ethanol-90% ethylacetate (by volume), 20 ml. of saturated sodium carbonate solution and20 g. solid sodium carbonate. The free base is converted to thehydrochloride salt by dissolving in 100 ml. of absolute ethanol, adding10 ml. 9.6 N HCl and precipitated by addition to 1 l. of ethyl ether.After three precipitations from ethanol-ethyl ether as carried outabove, 15.1 g. (15%) of the hydrochloride salt of the 2-acetamidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride is obtained,Rf = 0.57, thin layer chromatography [fluorescent silica gel platedeveloped with 50% methanol-50% benzene (by volume)].

Anal. calcd. for C₁₄ H₂₀ N₂ O₅.HCl: C, 50.52; H, 6.36; N, 8.41. Found:C, 50.49; H, 6.69, N, 8.49.

EXAMPLE 25 Preparation of 3-acetamidopropylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate hydrate

Thionyl chloride, 275 ml., is added to 250 g. ofL-3-(3,4-dihydroxyphenyl)-2-methylalaninate sesquihydrate at 25° C. andthe mixture is heated on the steam bath. After heating for two hours,the thick reaction mixture is diluted with 7.5 ml. dimethylformamidedissolved in 25 ml. of benzene and stirred on the steam bath until gasevolution ceases. 100 Ml. of benzene is added and the crude sulfurousacid ester is removed by filtration, washed with 100 ml. of benzene, 100ml. of chloroform and 100 ml. of ether and dried under reduced pressureto give 280 g. of the sulfurous acid ester intermediate, m.p. 199° C.dec.

A mixture of 13.7 g. of the crude sulfurous acid ester intermediate,24.98 g. (0.212 mole) of N-acetylpropanolamine and 2 g. of anhydrousdimethylformamide is stirred on the steam bath for 20 hours and cooled.The reaction mixture is washed with six 200 ml. portions of ethyl ether,four 200 ml. portions of methylene chloride and dried under reducedpressure. The semi-solid material remaining is stirred with 200 ml. 20%ethanol-30% ethyl acetate (by volume), 20 ml. saturated sodium carbonatesolution and 20 g. solid sodium carbonate. The organic extract is driedover anhydrous magnesium sulfate, filtered and the filtrate added to asolution of 3.2 g. oxalic acid in 50 ml. ethanol. Removal of solventsunder reduced pressure is then accomplished and the product isprecipitated by dissolving it in 50 ml. of ethanol and adding 500 ml. ofethyl ether. The product is again precipitated by dissolving in 50 ml.of ethanol and adding 500 ml. of ethyl acetate to give 3-acetamidopropylL-3-(3,4-dihydroxypheny)-2-methylalaninate hydrogen oxalate hydrate, Rf= 0.45, thin layer chromatography [fluorescent silica gel platedeveloped with 25% methanol-75% chloroform (by volume)].

Anal. calcd. for C₁₅ H₂₂ N₂ O₅.C₂ H₂ O₄.H₂ O: C, 48.80; H, 6.26; N,6.69. Found: C, 48.73; H, 6.85; N, 6.68.

EXAMPLE 26 Preparation of 2-methylthioethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate

Thionyl chloride, 275 ml., is added to 250 g. ofL-3-(3,4-dihydroxyphenyl)-2-methylalaninate sesquihydrate at 25° C. andthe mixture is heated on the steam bath. After heating for two hours,the thick reaction mixture is diluted with 7.5 ml. dimethylformamide in25 ml. of benzene and stirred on the steam bath until gas evolutionceases. 100 Ml. of benzene is added and the crude sulfurous acid esteris removed by filtration, washed with 100 ml. of benzene, 100 ml. ofchloroform and 100 ml. of ether and dried under reduced pressure to give280 g. of the sulfurous acid ester intermediate, m.p. 199° C. dec.

A mixture of 30 g. of the crude sulfurous acid ester, 34.6 g. (0.375mole) of 2-hydroxyethylmethylsulfide and 6 g. of anhydrousdimethylformamide is stirred on the steam bath for 28 hours and cooled.The reaction mixture is washed with four 100 ml. portions of ethyl etherand three 100 ml. portions of methylene chloride. The remaining materialis stirred with 250 ml. of 20% ethanol-80% ethyl acetate (by volume), 30ml. saturated sodium carbonate solution and 60 g. solid sodium carbonateand then filtered. The insoluble material is washed with three 250 ml.portions of 20% ethanol-80% ethyl acetate (by volume), combined with thefirst ethanol-ethyl acetate extract and dried over anhydrous magnesiumsulfate. After filtering, solvents are removed under reduced pressureand the residue is chromatographed over silica gel. A total of 2.3 g. ofproduct is eluted with a 25% methanol-75% chloroform (by volume)mixture. This product is converted to the oxalate salt by adding it to asolution of 1.3 g. of oxalic acid in 25 ml. of ethanol followed byprecipitation with sufficient ethyl ether. After three moreprecipitations using ethanol to dissolve the product and ethyl ether toprecipitate it, 300 mg. of the 2-methylthioethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate isobtained, homogeneous upon thin layer chromatography [fluorescent silicagel plate developed with 25% methanol-75% chloroform (by volume)] Rf =0.83, m.p. 85°-90° C. dec.

Anal. calcd. for C₁₃ H₁₉ NO₄ S.C₂ H₂ O₄ : C, 47.99; H, 5.64; N, 3.73.Found: C, 48.00; H, 6.10; N, 4.07.

EXAMPLE 27 A. Preparation ofD,L-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine hydrochloride

A mixture of 38.6 g. (0.155 mole) ofracemic-3-(3,4-dihydroxyphenyl)-2-methylalanine hydrochloride and 74 g.(0.321 mole) of dichlorodiphenylmethane is immersed with slow stirringin a preheated oil bath at 190° C. After reaction has started, thereaction mixture is stirred rapidly for six minutes at 190° C., removedfrom the hot oil bath and allowed to cool to 25°-30° C. The crudeproduct from 6 runs is combined, slurried with 2 l. of diethyl ether,filtered, washed with an additional 2 l. of diethyl ether and dried at30° C. under 50 mm. pressure. The solid is recrystallized by dissolvingthe product in ethanol and adding ethyl acetate to precipitateD,L-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine hydrochloride.

B. Preparation ofD,L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylanlanine

A mixture of 175 g. (0.425 mole) ofracemic-3(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninehydrochloride, 1750 ml. of acetone and 1750 ml. of water is stirredunder nitrogen at a temperature below 10° C. while the pH is adjusted to12.0 by the slow addition of a 10% sodium hydroxide solution.Carbobenzyloxy chloride, 93 g. (0.545 mole) is added dropwise over 5-7minutes to the reaction mixture at 20°-30° C. accompanied by thesimultaneous addition of a 10% sodium hydroxide solution to maintain apH of 12.0-12.2. After addition of the carbobenzyloxy chloride iscomplete, the reaction mixture is stirred at 25°-30° C. for three hours.Most of the acetone is then removed under reduced pressure at 25° to 35°C. to precipitate the sodium salt of the desired N-carbobenzyloxyderivative. The sodium salt is extracted into 1.5 l. of ethyl acetate,washed with 200 ml. of 5% sodium hydroxide solution and 200 ml. of asaturated sodium chloride solution and then dried over magnesiumsulfate. After adding 17.5 g. of decolorizing carbon and filteringthrough a magnesium sulfate pad, solvents are removed under reducedpressure at 25° to 35° C. The residue is slurried two times with 1 l. ofa 20% ethyl ether-80% hexane (by volume) solution and filtered to givethe sodium salt of the desired N-carbobenzyloxy derivative. This sodiumsalt is dissolved in 1.5 l. of ethyl acetate, cooled to 10° C. andacidified to pH 2 with 6 N hydrochloric acid. The ethyl acetate extractis washed with 200 ml. of a saturated sodium chloride solution, driedover magnesium sulfate, filtered and concentrated under reduced pressureat 25° to 35° C. The N-carbobenzyloxy derivative is dried further at25°-30° C. and 0.2-0.3 mm. Hg to giveD,L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine.

C. Preparation of D,L-succinimidomethylN-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 13.5 g. (0.0265 mole) ofD,L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,2.7 g. (0.027 mole) of triethylamine and 5.19 g. (0.029 mole) ofN-bromomethylsuccinimide in 35 ml. of dry dimethylformamide is stirredat 25°-30° C. for 16 hours. The reaction mixture is poured into 400 ml.of ice water and the product extracted into 200 ml. of a 50%chloroform-50% diethyl ether (by volume) mixture. The organic extract iswashed with 50 ml. of a dilute (5%) sodium carbonate solution and 50 ml.of a saturated sodium chloride solution and then dried over anhydrousmagnesium sulfate to remove water. After filtering and concentratingunder reduced pressure, the residue is recrystallized. Recrystallizationis accomplished by dissolving the product in ethanol and adding hexaneto precipitate D,L-succinimidomethylN-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate.

D. Preparation of D,L-succinimidomethyl3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate

A suspension of 6.6 g. (0.0106 mole) of racemic succinimidomethylN-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninatein 180 ml. of absolute ethanol and 9 ml. of a 9.6 N ethanolic-anhydroushydrogen chloride solution is hydrogenated with 3.3 g. of a 10%palladium-on-carbon catalyst at an initial pressure of 30 p.s.i. untilhydrogen uptake is complete. After removal of catalyst by filtration,the filtrate is concentrated under reduced pressure. The residue isextracted with 50 ml. of benzene and then 50 ml. of ethyl acetate. Theinsoluble solid is then shaken with 50 ml. of a 10% ethanol-90% ethylacetate (by volume) mixture and 10 ml. of a saturated sodium carbonatesolution. After filtration, the filtrate is dried over anhydrousmagnesium sulfate, filtered and concentrated under reduced pressure togive D,L-succinimidomethyl 3-(3,4-dihydroxyphenyl)-2-methylalaninate asthe base.

E. Preparation of succinimidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate viarecrystallization of diastereomeric salts

A solution of 0.47 g. (3.1 mmole) of (-) tartaric acid in 10 ml. of a50% absolute ethanol-50% ethyl acetate (by volume) solution is addedunder nitrogen at 20°-25° C. to a solution of 1.0 g. (3.1 mmole) ofD,L-succinimidomethyl 3-83,4-dihydroxyphenyl)-2-methylalaninate in 10ml. of absolute ethanol. After warming the solution to 40°-60° C., ethylacetate is added to incipient cloudiness and then cooled slowly to 25°C. and finally stored at 5°-10° C. for 12 hours. The insoluble crudetartrate salt is removed by filtration and dried at 20°-25° C. and0.2-0.5 mm. pressure. This recrystallization procedure is repeated untilthe melting point and optical rotation of the tartrate salt areessentially constant.

The mother liquor from the initial crystallization is concentrated at15-20 mm. and 40°-50° C. The residue is shaken with 25 ml. of a 10%ethanol-90% ethyl acetate (by volume) mixture and 10 ml. of a saturatedsodium carbonate solution. After filtration, the filtrate is dried overanhydrous magnesium sulfate, filtered and concentrated at 15-20 mm. and40° C. to a gum. The residue is dissolved in 5 ml. of absolute ethanoland added under nitrogen to a solution of 0.3 g of (+) tartaric acid in10 ml. of a 50% absolute ethanol-50% ethyl acetate (by volume) solution.After warming the solution to 40°-60° C., ethyl acetate is added toincipient cloudiness and then cooled slowly to 25° C. and then stored at5°-10° C. for 14 hours. The insoluble crude tartrate salt is removed byfiltration. Repetition of this recrystallization procedure gives theother optical antipode of succinimidomethyl3-(3,4-dihydroxyphenyl)-2-methylalaninate as the tartrate salt.

The optically active tartrate salts are converted to the opticallyactive hydrochloride salts by the following method. The tartrate salt ofsuccinimido L-3-(3,4-dihydroxyphenyl)-2-methylalaninate is shaken with50 ml. of a 10% ethanol-90% ethyl acetate (by volume) mixture and 10 ml.of a saturated sodium carbonate solution. After filtration, the filtrateis dried over anhydrous magnesium sulfate, filtered and concentratedunder reduced pressure. The residue is redissolved in 25 ml. of absoluteethanol, treated with 5 ml. of a 9.6 N ethanolic-anhydrous hydrogenchloride solution and concentrated under reduced pressure to givesuccinimidomethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride hydrate, homogeneous upon thin layer chromatography[fluorescent silica gel plate, 30% methanol-70% benzene (by volume)solvent] with an observed Rf = 0.5.

EXAMPLE 28 Resolution of racemic pivaloyloxymethyl3-(3,4-dihydroxyphenyl)-2-methylalaninate by direct recrystallization

Racemic pivaloyloxymethyl 3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride is prepared as in Example 23.

Thirty grams of racemic pivaloyloxymethyl3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride are slurried at35° C. in 100 ml of 1.0 N hydrochloric acid. The excess solids arefiltered. The saturated solution is then seeded at 35° C. withpivaloyloxymethyl D-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride hydrate. The mixture is cooled to 20° C. in 30 minutes andallowed to stand at 20° C. for 0.5 hour. The separated material isisolated by filtration, washed twice with 5 ml. cold water and dried at0.1-0.5 mm. and 20°-25° C. for 20 hours to give pivaloyloxymethylD-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate.

The mother liquor from the preceding step is heated to 35° C. and isseeded at 35° C. with pivaloyloxymethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride. The mixtureis then cooled to 20° C. over 30 minutes and allowed to stand at 20° C.for 0.5 hour. The precipitated material is isolated by filtration,washed twice with 5 ml. cold water and dried at 0.1-0.5 mm. and 20°-25°C. for 20 hours to give pivaloyloxymethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate.

EXAMPLE 29 A. Preparation of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride dihydrate(β-isomer) by fractional crystallization

Ten grams of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride (α- andβ-isomer mixture) of Example 2 are dissolved in 50 ml. warm 95% ethanol(5% water), diluted to incipient cloudiness with anhydrous ether, seededand scratched to induce crystallization. After cooling at 5°-10° C. for12 hours, the precipitated solid is collected and dried at 70° C.Additional similar recrystallizations from 95% ethanol-5% water-ethylether (by volume) give material melting at 123°-126° C. (dec.). A finalrecrystallization from 95% ethanol affords α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride dihydrate(β-isomer) as the dihydrate melting at 129°-131° C. (dec.) (dried at 70°C. overnight), homogeneous upon thin layer chromatography [fluorescentsilica gel plate, 50% methanol-50% benzene (by volume) solvent], Rf =0.7.

B. Preparation of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate(α-isomer)

The mother liquor from the first crystallization of the β-isomer ofα-succinimidoethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride hydrate which is rich in the corresponding α-isomer isconcentrated at 15-20 mm. and 40°-45° C. The residue is dissolved in 20ml. warm 95% ethanol (5% water), diluted to incipient cloudiness withethyl acetate, seeded and scratched to precipitate the enriched α-isomerof α-succinimidoethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride hydrate. Additional precipitations from 95% ethanol (5%water) and ethyl acetate gives the α-isomer as the ethyl acetatesolvate, Rf = 0.7 [thin layer chromatography, fluorescent silica gelplate, 50% methanol-50% benzene (by volume) solvent].

EXAMPLE 30 Preparation of pivaloyloxymethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 0.95 g. (4.0 mmole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.61 g.(4.06 mmole) of pivaloyloxymethyl chloride in 5 ml. dimethylsulfoxide isstirred at 20°-25° C. for 23 hours. The solution is diluted with 10 ml.distilled water and passed through a column containing 5 g. of weaklybasic anion exchange resin on the base cycle. After elution with waterfractions, the fractions giving a positive ferric chloride test arecombined and added to a column of 3 g. of weakly acidic cation exchangeresin on the acid cycle. UnreactedL-3-(3,4-dihydroxyphenyl)-2-methylalanine is eluted with distilled wateruntil a negative ferric chloride test is obtained, the ester is theneluted with 1 N acetic acid. The ester fraction, 50 ml. (pH 3.2), isacidified to pH 2.0 with 1 N hydrochloric acid and lyophilized at0.1-0.3 mm. for 20 hours to give pivaloyloxymethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride as the aceticacid solvate.

Anal. calcd. for C₁₆ H₂₃ NO₆.HCl.1/3HC₂ H₄ O₂ : C, 52.11; H, 6.69; N,3.58. Found: C, 52.11; H, 6.49; N, 3.73.

EXAMPLE 31 Preparation of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 0.95 g. (4.0 mmole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.65 g. (4.0mmole) of N-(α-chloroethyl)-succinimide in 5 ml. dimethylsulfoxide isstirred at 20°-25° C. for 23 hours. The solution is diluted with 10 ml.distilled water and passed through a column containing 5 g. of weaklybasic anion exchange resin on the basic cycle. After elution with waterfractions, the fractions giving a positive ferric chloride test arecombined and added to a column of 3 g. of a weakly acidic cationexchange resin on the acid cycle. UnreactedL-3-(3,4-dihydroxyphenyl)-2-methylalanine is eluted with distilled wateruntil a negative ferric chloride test is obtained and the ester is theneluted with 1 N acetic acid. The ester fraction, 55 ml. (pH 3.2), istreated with 1 N hydrochloric acid to pH 2.0 and lyophilized at 0.1-0.3mm. for 20 hours to give α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride acetic acidsolvate.

Anal. calcd. for C₁₆ H₂₀ N₂ O₆.HCl.1/3C₂ H₄ O₂ : C, 50.96; H, 5.73; N,7.13. Found: C, 50.48; H, 6.13; N, 6.77.

EXAMPLE 32 Preparation of 3-acetamidopropylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate hydrate

Thionyl chloride, 275 ml., is added to 250 g. ofL-3-(3,4-dihydroxyphenyl)-2-methylalaninate sesquihydrate at 25° C. andthe mixture is heated on the steam bath. After heating for two hours,the thick reaction mixture is diluted with 7.5 ml. dimethylformamidedissolved in 25 ml. of benzene and stirred on the steam bath until gasevolution ceases. 100 Ml. of benzene is added and the crude sulfurousacid ester is removed by filtration, washed with 100 ml. of benzene, 100ml. of chloroform and 100 ml. of ether and dried under reduced pressureto give 280 g. of the sulfurous acid ester intermediate, m.p. 199° C.dec.

A mixture of 13.7 g. of the crude sulfurous acid ester intermediate,24.98 g. (0.212 mole) of N-acetylpropanolamine and 2 g. of anhydrousdimethylformamide is stirred on the steam bath for 20 hours and cooled.The reaction mixture is washed with six 200 ml. portions of ethyl ether,four 200 ml. portions of methylene chloride and dried under reducedpressure. The semi-solid material remaining is stirred with 200 ml. 20%ethanol-80% ethyl acetate (by volume), 20 ml. saturated sodium carbonatesolution and 20 g. solid sodium carbonate. The organic extract is driedover anhydrous magnesium sulfate, filtered and the filtrate added to asolution of 3.2 g. oxalic acid in 50 ml. ethanol. Removal of solventsunder reduced pressure is then accomplished and the product isprecipitated by dissolving it in 50 ml. of ethanol and adding 500 ml. ofethyl ether. The product is again precipitated by dissolving in 50 ml.of ethanol and adding 500 ml. of ethyl acetate of give 3-acetamidopropylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate hydrate, Rf= 0.45, thin layer chromatography [fluorescent silica gel platedeveloped with 25% methanol-75% chloroform (by volume)].

Anal. calcd. for C₁₅ H₂₂ N₂ O₅.C₂ H₂ O₄.H₂ O: C, 48.80; H, 6.26; N,6.69. Found: C, 48.73; H, 6.85; N, 6.68.

EXAMPLE 33 Preparation of 2-acetamidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A slurry of 88.3 g. (0.30 mole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine hydrochloride ethanol solvate(by concentration of an ethanolic solution of the hydrochloride underreduced pressure) and 146.4 g. (1.42 mole) of N-acetylethanolamine,under nitrogen, is warmed to 104°-108° C. Thionyl chloride, 84.8 g.(0.713 mole) is added over 15 minutes with stirring. The reactionmixture foams vigorously during the addition. After addition iscomplete, the reaction mixture is stirred at 104°-108° C. for 18 hours.Additional thionyl chloride, 42.4 g. (0.357 mole) is added over sevenminutes. The reaction mixture is allowed to stir at 104°-108° C. foranother 31/2 hours, then cooled to 30° C. and concentrated under reducedpressure to yield a viscous oil. This oil is slurried with 100 ml. ofchloroform and the chloroform removed under reduced pressure. This isrepeated three more times and then the oil is washed with 100 ml. ofbenzene which is decanted. The residue is dissolved in 700 ml. ofisopropanol and added to 6 l. of ethyl ether. The precipitate whichforms is washed with 500 ml. of ethyl ether and shaken with 6 l. of 10%ethanol-90% ethyl acetate (by volume), 150 ml. of saturated sodiumcarbonate solution and 100 g. of sodium carbonate. The organic extractis dried over anhydrous magnesium sulfate, filtered and concentratedunder reduced pressure to give the free base of the acetamidoethylester. This base is treated with 15 g. of fumaric acid in 300 ml. ofisopropanol and the fumarate salt precipitated by adding sufficientethyl ether. The fumarate salt is precipitated once more fromisopropanol by adding sufficient ethyl ether and then converted back tothe free base as before by shaking with 200 ml. of 10% ethanol-90% ethylacetate (by volume), 20 ml. of saturated sodium carbonate solution and20 g. solid sodium carbonate. The free base is converted to thehydrochloride salt by dissolving in 100 ml. of absolute ethanol, adding10 ml. 9.6 N HCl and precipitated by addition to 1 l. of ethyl ether.After three precipitations from ethanol-ethyl ether as carried outabove, 2-acetamidoethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride is obtained, Rf = 0.57, thin layer chromatography[fluorescent silica gel plate developed with 50% methanol-50% benzene(by volume)].

Anal. calcd. for C₁₄ H₂₀ N₂ O₅.HCl: C, 50.52; H, 6.36; N, 8.41. Found:C, 50.49; H, 6.69; N, 8.49.

EXAMPLE 34 A. Preparation of L-3-(3,4-diacetoxyphenyl)-2-methylalaninehydrochloride

To a mixture of 320 ml. glacial acetic acid and 24 ml. acetyl chlorideis added in one portion 69.4 g. (0.291 mole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate. The temperatureof the reaction mixture rises to approximately 50° C. and a clearsolution results. At this temperature, an additional 85 ml. of acetylchloride is added over 10 minutes. The resulting clear, pale yellowsolution is allowed to stand at 20°-25° C. for 14 hours. Anhydrous ethylether, 400 ml., is added over 15 minutes. When addition is almostcomplete, a white solid begins to precipitate. The mixture is stirred at20°-25° C. for 30 minutes, at 5°-10° C. for 1 hour and then cooled at-10° C. for 2 hours. The solid is removed by filtration, suspended in150 ml. of 30% acetic acid-70% ethyl ether (by volume), filtered andwashed with 500 ml. ethyl ether. After drying at 70° C. for 2 hours,83.7 g. (88%) of L-3-(3,4-diacetoxyphenyl)-2-methylalaninehydrochloride, m.p. 196.0°-197.0° C., is obtained.

B. Preparation of L-3-(3,4-diacetoxyphenyl)-2-methylalanyl chloridehydrochloride

A mixture of 6.60 g. (0.020 mole) ofL-3-(3,4-diacetoxyphenyl)-2-methylalanine hydrochloride and 40 ml.thionyl chloride is stirred at 60° C. for 2 hours until solution iscomplete. Excess thionyl chloride is removed at 15-20 mm. and 40°-50° C.Methylene chloride, 50 ml., is added and the mixture is reconcentratedat 15-20 mm. and 40°-50° C. This is repeated once more with another 50ml. of methylene chloride. After drying at 0.2-0.5 mm. and 40° C. for 30minutes, L-3-(3,4-diacetoxyphenyl)-2-methylalanyl chloride is obtained.

C. Preparation of succinimidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate

A solution of 3.50 g. (10 mmole) ofL-3-(3,4-diacetoxyphenyl)-2-methylalanyl chloride hydrochloride in 20ml. chloroform is added to a solution of 3.87 g. (30 mmole) ofN-hydroxymethylsuccinimide in 20 ml. chloroform at 25° C. After stirringat reflux for 20 hours, most of the chloroform is removed at 15-20 mm.and 30°-40° C. The residue is diluted with 10 ml. of 1 N hydrochloricacid and extracted with two 20 ml. portions of ethyl ether. The aqueousextract is stirred under nitrogen at 20°-25° C. for 5 hours. Afterlyophilization at 0.1-0.3 mm. for 20 hours, the residue is treated with50 ml. of a 10% ethanol-90% ethyl acetate (by volume) solution, 5 ml. ofa saturated sodium carbonate solution and 5 g. of solid sodiumcarbonate. After filtration, the filtrate is dried over anhydrousmagnesium sulfate, filtered and concentrated at 15-20 mm. and 30°-40° C.The residue is redissolved in 25 ml. of absolute ethanol, treated with 5ml. of a 9.6 N ethanolic-anhydrous hydrogen chloride solution andconcentrated under reduced pressure to give succinimidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate,homogeneous upon thin layer chromatography [fluorescent silica gelplate, 30% methanol-70% benzene (by volume) solvent] with an observed Rf= 0.5.

EXAMPLE 35 A. Preparation of the N-carboxyanhydride ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine

Phosgene gas is bubbled through a mixture of 9.0 g. (0.038 mole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate in 500 ml.tetrahydrofuran for 25 minutes until the solution is saturated. Duringthe addition, the temperature of the reaction mixture rises to 45° C.The solution is stirred with nitrogen gas bubbling through for anadditional 50 minutes. Insoluble material is removed by filteringthrough a diatomaceous earth pad and the filtrate is concentrated to anoil at 15-20 mm. pressure and 30°-35° C. The residue is dissolved in 75ml. ethyl acetate and hexane is added to the cloudpoint. After coolingfor several days at 0°-5° C., the precipitated solid is removed byfiltration and dried at 0.1-0.3 mm. pressure and 25° C. to give theN-carboxyanhydride of L-3-(3,4-dihydroxyphenyl)-2-methylalanine.

B. Preparation of succinimidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate

A solution of 2.37 g. (10 mmole) of the N-carboxyanhydride ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine and 1.29 g. (10 mmole) ofN-hydroxymethylsuccinimide is heated at reflux until all of theN-carboxyanhydride has reacted. After concentrating at 15-20 mm.pressure and 30°-40° C., the residue is extracted with 50 ml. of benzeneand then 50 ml. of ethyl acetate. The insoluble solid is then shakenwith 50 ml. of a 10% ethanol-90% ethyl acetate (by volume) mixture and10 ml. of a saturated sodium carbonate solution. After filtration, thefiltrate is dried over anhydrous magnesium sulfate, filtered andconcentrated under reduced pressure. The residue is redissolved in 25ml. of absolute ethanol, treated with 5 ml. of a 9.6 Nethanolic-anhydrous hydrogen chloride solution and concentrated underreduced pressure to give succinimidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate,homogeneous upon thin layer chromatography [fluorescent silica gelplate, 30% methanol-70% benzene (by volume) solvent] with an observed Rf= 0.5.

EXAMPLE 36 A. Preparation ofL-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine hydrochloride

A mixture of 19.3 g. (0.0777 mole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine hydrochloride and 37 g. (0.156mole) of dichlorodiphenylmethane is immersed with slow stirring in apreheated oil bath at 190° C. After reaction has started, as evidencedby vigorous gas evolution, the reaction mixture is stirred rapidly for 6minutes at 190° C., removed from the hot oil bath and allowed to cool to25°-30° C. The crude product from 12 runs is combined, slurried with 3l. of diethyl ether, filtered, washed with an additional 2 l. of diethylether and dried at 30° C. under 50 mm. pressure. Recrystallization isaccomplished by dissolving the product in ethanol and adding ethylacetate to precipitate the product. The procedure gives 255 g. (66.4%)of L-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine hydrochloride,m.p. 267°-268° C. dec.

B. Preparation of α-succinimidoethylL-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 1.4 g. (4.0 mmole) ofL-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine and 0.65 g. (4.0mmole) of N-(α-chloroethyl)-succinimide in 5 ml. dimethylsulfoxide isstirred at 20°-25° C. for 23 hours. Water, 150 ml., is added followed bya saturated sodium carbonate solution until a pH of 8 is obtained. Theproduct is extracted into 500 ml. of ethyl ether which is then washedwith four 25 ml. portions of water, dried over anhydrous magnesiumsulfate and filtered. Concentration at 15-20 mm. and 35°-40° C. givescrude α-succinimidoethylL-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate of sufficientpurity for use in the next step.

C. Preparation of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A suspension of 1.0 g. (2.0 mmole) of α-succinimidoethylL-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 25 ml. of25% absolute ethanol-75% ethyl acetate (by volume) solution ishydrogenated with 1.0 g. of 10% palladium-on-carbon catalyst at aninitial pressure of 40 p.s.i. and room temperature for 23 hours. Thecatalyst is filtered and the filtrate evaporated under reduced pressureat 30° to 40° C. The residue is dissolved in 50 ml. of 10% ethanol-90%ethyl acetate (by volume) solution and stirred with 5 ml. of saturatedsodium carbonate solution and approximately 5 g. of anhydrous sodiumcarbonate for 10 minutes. After filtration, the filtrate is dried overanhydrous magnesium sulfate, filtered and evaporated to dryness underreduced pressure. The residue is dissolved in 20 ml. of dry chloroform,the solution is cooled in an ice bath and saturated with hydrogenchloride gas for 15 minutes. The solid is collected, washed bysuspension in 25 ml. of anhydrous ether three times and then slurried in25 ml. of ethyl acetate under N₂ in a stoppered flask at roomtemperature overnight. The insoluble solid is removed by filtration,stirred with 30 ml. hexane for 2 hours and dried in a vacuum desiccatorover CaCl₂ to give α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride as a mixtureof α- and β-isomers, observed Rf = 0.7 upon thin layer chromatography[fluorescent silica gel plate, 50% methanol-50% benzene (by volume)solvent].

EXAMPLE 37 A. Preparation of L-3-(3,4-diacetoxyphenyl)-2-methylalaninehydrochloride

To a mixture of 320 ml. glacial acetic acid and 24 ml. acetyl chlorideis added in one portion, 69.4 g. (0.291 mole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate. The temperatureof the reaction mixture rises to approximately 50° C. and a clearsolution results. At this temperature, an additional 85 ml. of acetylchloride is added over 10 minutes. The resulting clear, pale yellowsolution is allowed to stand at 20°-25° C. for 14 hours. Anhydrous ethylether, 400 ml., is added over 15 minutes. When addition is almostcomplete, a white solid begins to precipitate. The mixture is stirred at20°-25° C. for 30 minutes, at 5°-10° C. for 1 hour and then cooled at-10° C. for 2 hours. The solid is removed by filtration, suspended in150 ml. of 30% acetic acid-70% ethyl ether (by volume), filtered andwashed with 500 ml. ethyl ether. After drying at 70° C. for 2 hours,83.7 g. (88%) of L-3-(3,4-diacetoxyphenyl)-2-methylalaninehydrochloride, m.p. 196.0°-197.0° C., is obtained.

B. Preparation of α-succinimidoethylL-3-(3,4-diacetoxyphenyl)-2-methylalaninate hydrochloride

A solution of 1.66 g. (5 mmole) ofL-3-(3,4-diacetoxyphenyl)-2-methylalanine hydrochloride, 0.51 g. (5mmole) of triethylamine and 0.81 g. (5 mmole)N-(α-chloroethyl)-succinimide in 5 ml. of dimethyl sulfoxide is stirredat 20°-25° C. for 20-24 hours. Dimethyl sulfoxide is removed by stirringwith 20 ml. ethyl ether for several minutes and then decanting off theethyl ether. This extraction process is carried out three times. Theresidue is dissolved in 10 ml. of absolute ethanol and the productprecipitated by the addition of excess ethyl ether. This precipitationprocess is repeated two more times to give pure α-succinimidoethylL-3-(3,4-diacetoxyphenyl)-2-methylalaninate hydrochloride.

EXAMPLE 38 Preparation of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 1.8 g. (3.94 mmole) of α-succinimidoethylL-3-(3,4-diacetoxyphenyl)-2-methylalaninate hydrochloride (of Example37) in 10 ml. of 1 N hydrochloric acid is stirred under nitrogen at20°-25° C. for 5 hours. After lyophilization at 0.1-0.3 mm. for 20hours, the residue is treated with 50 ml. of a 10% ethanol-90% ethylacetate (by volume) solution, 5 ml. of a saturated sodium carbonatesolution and 5 g. of solid sodium carbonate. After filtration, thefiltrate is dried over anhydrous magnesium sulfate, filtered andevaporated to dryness under reduced pressure. The residue is dissolvedin 20 ml. of dry chloroform, the solution is cooled in an ice bath andsaturated with hydrogen chloride gas for 15 minutes. The solid iscollected, washed by suspension in 25 ml. of anhydrous ethyl ether threetimes and then slurried in 25 ml. of ethyl acetate under N₂ in astoppered flask at room temperature overnight. The α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride is collectedand dried in a vacuum desiccator over CaCl₂ to give the hydrochloride asa mixture of α- and β-isomers, observed Rf = 0.7 upon thin layerchromatography [fluorescent silica gel plate, 50% methanol-50% benzene(by volume) solvent].

EXAMPLE 39 A. Preparation of N-(1-chloroethyl)-maleimide

Stannic chloride, 5.20 g. (0.020 mole) is added to a solution of 49.2 g.(0.40 mole) of n-vinylmaleimide in 1 l. of carbon tetrachloride and themixture is stirred while saturating with hydrogen chloride for 6 hoursat 20°-30° C. After 24 hours, the mixture is resaturated with hydrogenchloride for 1.5 hours. At the end of 48 hours, the solution is decantedand the gummy residue is washed with ten 100 ml. portions of carbontetrachloride. The combined extracts are slurried with 10 g. ofdiatomaceous earth, filtered and the filtrate concentrated under reducedpressure to approximately 400 ml. The N-(1-chloroethyl)-maleimide isfiltered and dried at 20°-30° C.

B. Preparation of α-maleimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 0.95 g. (4.0 mmole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.64 g. (4.0mmole) of N-(α-chloroethyl)-maleimide in 5 ml. dimethylsulfoxide isstirred at 20°-25° C. for 23 hours. The solution is diluted with 10 ml.distilled water and passed through a column containing 5 g. of weaklybasic anion exchange resin on the basic cycle. After elution with waterfractions, the fractions giving a positive ferric chloride test arecombined and added to a column of 3 g. of a weakly acidic cationexchange resin on the acid cycle. UnreactedL-3-(3,4-dihydroxyphenyl)-2-methylalanine is eluted with distilled wateruntil a negative ferric chloride test is obtained and the ester is theneluted with 1 N acetic acid. The ester fraction, 55 ml. (pH 3.2), istreated with 1 N hydrochloric acid to pH 2.0 and lyophilized at 0.1-0.3mm. for 20 hours to give α-maleimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride.

C. Preparation of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 1.0 g. (2.7 mmole) of α-maleimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride in 25 ml.absolute ethanol is hydrogenated with 1.0 g. of 10% palladium-on-carboncatalyst at atmospheric pressure and 25° C. until one equivalent ofhydrogen is taken up. The catalyst is filtered and the filtrateevaporated under reduced pressure at 30° to 40° C. The residue isdissolved in 50 ml. of 10% ethanol-90% ethyl acetate (by volume)solution and stirred with 5 ml. of saturated sodium carbonate solutionand approximately 5 g. of anhydrous sodium carbonate for 10 minutes.After filtration, the filtrate is dried over anhydrous magnesiumsulfate, filtered and evaporated to dryness under reduced pressure. Theresidue is dissolved in 20 ml. of dry chloroform, the solution is cooledin an ice bath and saturated with hydrogen chloride for 15 minutes. Thesolid is collected, washed by suspension in 25 ml. of anhydrous etherthree times and then slurried in 25 ml. of ethyl acetate under N₂ in astoppered flask at 20°-25° C. overnight. The insoluble solid is removedby filtration, stirred with 30 ml. hexane for 2 hours and dried in avacuum desiccator over CaCl₂ to give α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride as a mixtureof α- and β-isomers, observed Rf = 0.7 upon thin layer chromatography[fluorescent silica gel plate, 50% methanol-50% benzene (by volume)solvent].

EXAMPLE 40 A. Preparation of α-chloroethyl3-chloro-2,2-dimethylpropionate

Zinc chloride, 400 mg. is fused at 0.2-0.5 mm. pressure and cooled to25°-30° C. under nitrogen. 3-Chloro-2,2-dimethylpropionylchloride, 62 g.(0.40 mole) is added to the fused zinc chloride followed byacetaldehyde, 19.2 g. (0.44 mole). During addition of the acetaldehyde,which is done as rapidly as possible, the reaction mixture is stirredand cooled to prevent loss of acetaldehyde due to the exothermic natureof the reaction. After heating at reflux for 1 hour, distillation givesα-chloroethyl 3-chloro-2,2-dimethylpropionate.

B. Preparation of α-(3-chloro-2,2-dimethylpropionyloxy)ethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 0.95 g. (4.0 mmole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.81 g.(4.06 mmole) of α-chloroethyl 3-chloro-2,2-dimethylpropionate in 5 ml.dimethylsulfoxide is stirred at 20°-25° C. for 23 hours. The solution isdiluted with 10 ml. distilled water and passed through a columncontaining 5 g. of weakly basic anion exchange resin on the base cycle.After elution with water fractions, the fractions giving a positiveferric chloride test are combined and added to a column of 3 g. ofweakly acidic cation exchange resin on the acid cycle. UnreactedL-3-(3,4-dihydroxyphenyl)-2-methylalanine is eluted with distilled wateruntil a negative ferric chloride test is obtained, the ester is theneluted with 1 N acetic acid. The ester fraction, 50 ml. (pH 3.2), isacidified to pH 2.0 with 1 N hydrochloric acid and lyophilized at0.1-0.3 mm. for 20 hours to giveα-(3-chloro-2,2-dimethylpropionyloxy)-ethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride as the aceticacid solvate.

C. Preparation of α-pivaloyloxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 1.5 g. (3.66 mmole) ofα-(3-chloro-2,2-dimethylpropionyloxy)-ethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride in 20 ml.absolute ethanol is hydrogenated with 1.0 g. of a 10%palladium-on-carbon catalyst at 20°-25° C. and atmospheric pressureuntil one equivalent of hydrogen is taken up. After removing catalyst byfiltration, ethanol is removed at 15-20 mm. and 30°-35° C. The residueis dissolved in 40 ml. ethyl acetate, stirred briefly with a mixture of2 g. of solid sodium carbonate and 2 ml. saturated sodium carbonatesolution and dried over anhydrous magnesium sulfate. After filtering, 1ml. of 9.6 N ethanolic-anhydrous hydrogen chloride is added and thesolution concentrated under reduced pressure to dryness. Further dryingat 65° C. and 0.2 mm. pressure gives the α-pivaloyloxyethyl esterhydrochloride.

EXAMPLE 41 A. Preparation of benzyl succinamate

A mixture of 23.4 g. (0.20 mole) of succinamic acid, 25.4 g. (0.20 mole)of benzyl chloride, 20.2 g. (0.20 mole) triethylamine and 250 ml.dimethylformamide is stirred at 95° C. for 20 hours. The reactionmixture is diluted with 500 ml. water and the product extracted into two200 ml. portions of ethyl ether. The combined ether extracts are washedwith two 50 ml. portions of saturated sodium bicarbonate solution, thentwo 50 ml. portions of water and dried over anhydrous magnesium sulfate.After filtering, the solution is concentrated at 15-20 mm. and 40° C. togive benzyl succinamate.

B. Preparation of benzyl N-hydroxymethylsuccinamate

To a stirred solution of 20.7 g. (0.10 mole) of benzylsuccinamate in 150ml. ethyl acetate at 25° C. is added 3.0 g. of paraformaldehyde and 1ml. of a 20% (by weight) solution of ethanolic potassium hydroxide.After stirring at 25° C. for 20 hours, hexane is added to the cloudpointand the mixture is cooled at 5° C. for 24 hours. Solvents are decantedoff and the residue is washed with 25 ml. hexane to give benzylN-hydroxymethylsuccinamate.

C. Preparation of benzyl N-chloromethylsuccinamate

A solution of 24.2 g. (0.10 mole) of benzyl N-hydroxymethylsuccinamateand 28.9 g. (0.11 mole) of triphenylphosphine in 500 ml. carbontetrachloride is stirred at reflux for 12 hours. After filtering andwashing the precipitate with benzene, the organic solvents are removedat 15-20 mm. and 30°-40° C. to give benzyl N-chloromethylsuccinamate ofsufficient purity for use in the next step.

D. Preparation of benzylsuccinamidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine

A solution of 10.2 g. (0.020 mole) ofL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine,2.02 g. (0.020 mole) of triethylamine and 5.12 g. (0.020 mole) of benzylN-chloromethylsuccinamate in 20 ml. dimethylformamide is stirred at 70°C. for 5 hours, then at 20°-30° C. for 5 hours and finally poured into200 ml. of water. The product is extracted with three 100 ml. portionsof ethyl acetate, washed with 50 ml. of a 5% sodium hydroxide solution,50 ml. of water and 50 ml. of saturated sodium chloride solution anddried over anhydrous magnesium sulfate. After filtering, solvents areremoved at 15-20 mm. and 30°-40° C. to give benzylsuccinamidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine.

E. Preparation of succinamidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 13.8 g. (0.0189 mole) of benzylsuccinamidomethylL-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninein 130 ml. of 25% absolute ethanol-75% ethyl acetate (by volume) ishydrogenated with 5 g. of a 10% palladium-on-carbon catalyst at 20°-25°C. and an initial pressure of 40 p.s.i. for 18 hours until hydrogenuptake ceases. After removing catalyst by filtration and concentratingto dryness under reduced pressure, the residue is dissolved in 200 ml.of a 10% absolute ethanol-90% ethyl acetate (by volume) solution andstirred with 5 ml. of a saturated sodium carbonate solution and excesssolid carbonate for 2 minutes. Ten grams of anhydrous magnesium sulfateare added and after a few minutes are removed by filtration. Solventsare removed under reduced pressure, the residue is washed with 25 ml. ofhexane and then 25 ml. of ethyl acetate and dried under reducedpressure. The residue is retreated with sodium carbonate as before toremove the last traces of α-methyl-3,4-dihydroxyphenylalanine andconverted to the hydrochloride salt with 3 ml. of 9.6 Nethanolic-anhydrous hydrogen chloride to give succinamidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride.

F. Preparation of succinimidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate

A mixture of 3.95 g. (10 mmole) of succinamidomethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride and 100 ml.acetyl chloride is stirred at 25° C. for 6 hours. After concentrating at15-20 mm. and 35° C., the residue is dissolved in 25 ml. of 1 Nhydrochloric acid and is stirred under nitrogen at 20°-25° C. for 5hours. After lyophilization at 0.1-0.3 mm. for 20 hours, the residue istreated with 50 ml. of a 10% ethanol-90% ethyl acetate (by volume)solution, 5 ml. of a saturated sodium carbonate solution and 5 g. ofsolid sodium carbonate. After filtration, the filtrate is dried overanhydrous magnesium sulfate, filtered and concentrated at 15-20 mm. and30°-40° C. The residue is redissolved in 25 ml. of absolute ethanol,treated with 5 ml. of a 9.6 N ethanolic-anhydrous hydrogen chloridesolution and concentrated under reduced pressure to givesuccinimidomethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride hydrate, homogeneous upon thin layer chromatography[fluorescent silica gel plate, 30% methanol-70% benzene (by volume)solvent] with an observed Rf = 0.5.

EXAMPLE 42 A. Preparation of 2-hydroxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 0.95 g. (4.0 mmole) ofL-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.51 g.(4.06 mmole) of 2-bromoethanol in 5 ml. dimethyl sulfoxide is stirred at60° C. for 5 hours and then allowed to cool to 20°-25° C. over 23 hours.The solution is diluted with 10 ml. distilled water and passed through acolumn containing 5 g. of weakly basic anion exchange resin on the basecycle. After elution with water fractions, the fractions giving apositive ferric chloride test are combined and added to a column of 3 g.of weakly acidic cation exchange resin on the acid cycle. UnreactedL-3-(3,4-dihydroxyphenyl)-2-methylalanine is eluted with distilled wateruntil a negative ferric chloride test is obtained, the ester is theneluted with 1 N acetic acid. The ester fraction, 50 ml. (pH 3.2), isacidified to pH 2.0 with 1 N hydrochloric acid and lyophilized at0.1-0.3 mm. for 20 hours to give 2-hydroxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride.

B. Preparation of 2-acetoxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate

A mixture of 1.0 g. (3.4 mmole) of 2-hydroxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride and 50 ml.acetyl chloride is stirred at 25° C. for 6 hours. After concentrating at15-20 mm. and 35° C., the residue is dissolved in 25 ml. of 1 Nhydrochloric acid and is stirred under nitrogen at 20°-25° C. for 5hours. After lyophilization at 0.1-0.3 mm. for 20 hours, the residue istreated with 50 ml. of a 10% ethanol-90% ethyl acetate (by volume)solution, 5 ml. of a saturated sodium carbonate solution and 5 g. ofsolid sodium carbonate. After filtering, the filtrate is dried overanhydrous magnesium sulfate, filtered and concentrated at 15-20 mm. and30°-40° C.

The residue is chromatographed on silica gel and eluted with 20%methanol-80% benzene (by volume). Recrystallization is accomplished bydissolving the ester in warm ethyl acetate and adding sufficientcyclohexane to precipitate the desired 2-acetoxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate, m.p. 114°-118° C. dec.

EXAMPLE 43 Preparation of 2-acetoxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate

A mixture of 1.0 g. (3.4 mmole) of 2-hydroxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride and 50 ml.methanesulfonylchloride is stirred at 25° C. for 6 hours. Concentrationat 15-20 mm. and 35° C. followed by drying at 0.1-0.5 mm. and 40° C.gives the crude methanesulfonyl derivative. To this is added 10 ml.dimethylsulfoxide and 6.6 g. (10 mmole) of lithium acetate and themixture is stirred at 60° C. for 6 hours. Following the addition ofexcess ethanolic-anhydrous hydrogen chloride solution, dimethylsulfoxideis removed by stirring three times with 50 ml. ethyl ether and decantingoff the ethyl ether. The residue is dissolved in 25 ml. of 1 Nhydrochloric acid and is stirred under nitrogen at 20°-25° C. for 1hour. After lyophilization at 0.1-0.3 mm. for 20 hours, the residue istreated with 50 ml. of a 10% ethanol-90% ethyl acetate (by volume)solution, 5 ml. of a saturated sodium carbonate solution and 5 g. ofsolid sodium carbonate. After filtration, the filtrate is dried overanhydrous magnesium sulfate, filtered and concentrated at 15-20 mm. and30°-40° C.

The residue is chromatographed on silica gel and eluted with 20%methanol-80% benzene (by volume). Recrystallization of the ester isaccomplished by dissolving it in ethyl acetate and adding sufficientcyclohexane to precipitate the desired 2-acetoxyethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate, m.p. 114°-118° C. dec.

EXAMPLE 44 Hard Gelatin Capsules

    ______________________________________                                                                 Gm.                                                  ______________________________________                                        succinimidomethyl L-3-(3,4-dihydroxyphenyl)-                                  2-methylalaninate hydrochloride hydrate                                                                  200                                                Cornstarch                 150                                                Magnesium stearate, powder  50                                                Talc                        50                                                ______________________________________                                    

The finely powdered ingredients are mixed thoroughly and thenencapsulated in 1000 two-piece hard gelatin capsules each containing 200mgs. of succinimidomethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride hydrate.

EXAMPLE 45 Tablets

1000 Tablets each containing 100 mgs. of α-succinimidoethylL-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride dihydrate(β-isomer) are prepared from the following ingredients:

    ______________________________________                                                                 Gm.                                                  ______________________________________                                        α-succinimidoethyl L-3-(3,4-dihydroxyphenyl)-                           2-methylalaninate hydrochloride dihydrate                                     (β-isomer)            100                                                Lactose                    50                                                 Starch                     50                                                 Calcium stearate           10                                                 Talc                       10                                                 ______________________________________                                    

The finely powdered ingredients are mixed thoroughly and then tabletedby a slugging procedure.

EXAMPLE 46 Hard Gelatin Capsules

Five thousand two-piece hard gelatin capsules, each containing 400 mg.of α-pivaloyloxyethyl L-3-(3,4-dihydroxyphenyl)-2-methylalaninatehydrochloride are prepared from the following ingredients:

    ______________________________________                                                                 Gm.                                                  ______________________________________                                        α-pivaloyloxyethyl L-3-(3,4-dihydroxyphenyl)-                           2-methylalaninate hydrochloride                                                                          2000                                               Lactose                    3000                                               Magnesium stearate         1000                                               Talc                       1000                                               ______________________________________                                    

The finely powdered ingredients are mixed thoroughly and thenencapsulated by conventional techniques.

EXAMPLE 47 Anti-Hypertensive Activity

The procedure for evaluating the anti-hypertensive activity of theactive agents comprises administering the compound either orally orintraperitoneally in spontaneously hypertensive rats of theWistar-Okamoto strain. Arterial pressure is recorded continuously inthese animals through an indwelling aortic catheter introduced throughthe caudal artery. The animals are allowed free movement in themetabolism cage during the measurements.

When the compounds of the present invention are tested orally, distinctanti-hypertensive activity is noted. The compounds also showanti-hypertensive activity when tested intraperitoneally. In someinstances the compounds show substantially more activity thanL-α-methyldopa.

Many other equivalent modifications will be apparent to those skilled inthe art from a reading of the foregoing without a departure from theinventive concept.

What is claimed is:
 1. A compound of the formula: ##STR22## wherein: nis 0, 1, 2, or 3,m is 0, 1, 2, or 3; A₁ and A₂ are individually H or alower alkanoyl group, R₁ and R₂ are individually H or alkyl of 1 to 3carbon atoms and R₃ is nicotinamido; or a pharmaceutically acceptablesalt thereof.
 2. A free base of the claim 1 compound.
 3. Apharmaceutically acceptable acid addition salt of the claim 1 compound.4. A compound of claim 1 having the formula: ##STR23##
 5. An ester ofthe L-isomer of an amino acid, substantially free of the D-isomer,having the formula: ##STR24## Wherein: n is 0, 1, 2, or 3;m is 0, 1, 3,or 3, R₁ and R₂ are individually H or alkyl of 1 to 3 carbon atoms andR₃ is nicotinamido; or a pharmaceutically acceptable acid addition saltthereof.
 6. A free base of the claim 5 ester.
 7. A pharmaceuticallyacceptable acid addition salt of the claim 5 ester.
 8. An ester of claim5 having the formula: ##STR25##
 9. A pharmaceutical composition fortreating hypertension comprising an inert pharmaceutically acceptablediluent and an effective amount of a compound of claim
 1. 10. Thepharmaceutical composition of claim 9 wherein said compound is presentin amounts of from about 1 mg to about 2000 mgs.
 11. The pharmaceuticalcomposition of claim 9 wherein said compound is present in amounts offrom about 5 mgs. to about 1,000 mgs.
 12. The pharmaceutical compositionof claim 9 wherein said compound is present in amounts of from about 10mgs. to about 500 mgs.
 13. The pharmaceutical composition of claim 9wherein said compound is2-nicotinamidoethyl-3-(3,4-dihydroxyphenyl)-2-methylalaninate.
 14. Apharmaceutical composition for treating hypertension comprising an inertpharmaceutically acceptable diluent and an effective amount of theL-isomer of an amino acid substantially free of an isomer having theformula: ##STR26## wherein n is 0, 1, 2, or 3;m is 0, 1, 2, or 3, R₁ andR₂ are individually H or alkyl of 1 to 3 carbon atoms and R₃ isnicotinamido, or a pharmaceutically acceptable acid addition saltthereof.
 15. The pharmaceutical composition of claim 14 wherein saidester is present in amounts of from about 1 mg. to about 2,000 mgs. 16.The pharmaceutical composition of claim 14 wherein said ester is presentin amounts of from about 5 mgs. to about 1,000 mgs.
 17. Thepharmaceutical composition of claim 14 wherein said ester is present inamounts of from about 10 mgs. to about 500 mgs.
 18. The pharmaceuticalcomposition of claim 14 wherein said ester is2-nicotinamidoethyl-3-L-(3,4-dihydroxyphenyl)-2-methylalaninate.